How Much Grout Do I Need for Tile? Calculator Guide

Running out of grout mid-project creates visible seam lines where you mix a new batch. The first batch has already started curing, so the second batch never quite matches in color or texture. You’ll see those lines forever. Buying too much wastes money because opened grout bags absorb moisture and turn into 25-pound chunks of concrete. This guide shows you exactly how much grout to buy.

The Quick Answer

For a 100 sq ft bathroom floor with 12×12 inch tiles and 1/8 inch joints:

• Grout needed: 2 bags (10 lb each)
• Grout type: Sanded (joints ≥1/8”)
• Cost estimate: $16–$30 total

For a 150 sq ft kitchen floor with the same tile: 3 bags (10 lb).

For a 60 sq ft bathroom floor with 6×6 inch tiles: 4 bags (10 lb) due to more grout lines.

The Grout Calculation Formula

Grout calculation requires determining what percentage of your floor is grout joints versus tile surface:

$\text{Grout Area Ratio} = 1 - \frac{\text{Tile Length} \times \text{Tile Width}}{(\text{Tile Length} + \text{Joint Width}) \times (\text{Tile Width} + \text{Joint Width})}$

This ratio multiplied by total floor area and joint depth gives you grout volume in cubic inches.

Step-by-Step Calculation

1. Calculate tile area: Length × Width (in inches)
2. Calculate tile plus joint area: (Length + Joint Width) × (Width + Joint Width)
3. Find grout ratio: 1 - (Tile Area ÷ Tile Plus Joint Area)
4. Calculate grout volume: Floor Area × Grout Ratio × Joint Depth
5. Convert to bags: Divide by coverage rate for your tile size and joint width

Example: 100 Sq Ft Floor with 12×12 Tiles

For 100 sq ft with 12×12 inch tiles, 1/4 inch joints, and 1/4 inch depth:

1. Tile area = 12 × 12 = 144 sq in
2. Tile plus joint = (12 + 0.25) × (12 + 0.25) = 12.25 × 12.25 = 150.06 sq in
3. Grout ratio = 1 - (144 ÷ 150.06) = 0.0404 (4.04% of floor is grout)
4. Total area = 100 sq ft × 144 = 14,400 sq in
5. Grout surface area = 14,400 × 0.0404 = 581.76 sq in
6. Grout volume = 581.76 × 0.25 depth = 145.44 cubic inches

A 10 lb bag typically covers 50–75 sq ft with standard 12×12 tiles and 1/8 inch joints. For 1/4 inch joints, coverage drops to 35–50 sq ft per bag. You need 2–3 bags for this 100 sq ft floor.

Grout Coverage Rates by Tile Size

Smaller tiles create exponentially more grout lines. A 2-inch mosaic has 36 times more linear grout footage than a 12-inch tile covering the same floor area.

Tile Size	Joint Width	Coverage per 10 lb Bag	100 Sq Ft Floor Needs
4×4 inch	1/8 inch	30–40 sq ft	3 bags
6×6 inch	1/8 inch	40–55 sq ft	2 bags
12×12 inch	1/8 inch	60–75 sq ft	1–2 bags
12×24 inch	1/8 inch	75–100 sq ft	1 bag
24×24 inch	1/8 inch	100–150 sq ft	1 bag
4×4 inch	1/4 inch	20–25 sq ft	4–5 bags
12×12 inch	1/4 inch	35–50 sq ft	2–3 bags
12×24 inch	1/4 inch	50–75 sq ft	1–2 bags

Coverage decreases by 30–50% when going from 1/8” to 1/4” joints

Sanded vs Unsanded Grout: The 1/8 Inch Rule

Grout type isn’t a preference. It’s determined by joint width. Use the wrong type and your installation fails.

Sanded Grout (for joints ≥1/8 inch)

What it is: Cement mixed with fine silica sand particles.

Why sand matters: Wide joints without sand shrink during curing, creating gaps that allow water penetration. Sand acts as aggregate, preventing shrinkage just like gravel prevents shrinkage in concrete.

When to use:

• Joints 1/8 inch to 1/2 inch wide
• All floor installations with standard joints
• Ceramic, porcelain, and unpolished natural stone
• Heavy traffic areas needing durability

Coverage: 50–75 sq ft per 10 lb bag for 12×12 tiles with 1/8 inch joints. Coverage decreases with smaller tiles or wider joints.

Cost: $8–15 per 10 lb bag, $15–25 per 25 lb bag.

Unsanded Grout (for joints <1/8 inch)

What it is: Pure cement-based grout with smooth texture.

Why no sand: Sand particles scratch polished marble, glass tile, and metal tile during application. Sand also can’t pack into narrow joints without leaving voids.

When to use:

• Joints under 1/8 inch (typically 1/16 inch)
• Polished marble and granite
• Glass tile and metal tile
• Vertical applications (walls, backsplashes) where sanded grout slumps

Coverage: Similar to sanded grout at same joint dimensions, but narrow joints mean less total grout consumed.

Cost: $10–18 per 10 lb bag.

The Borderline: Exactly 1/8 Inch Joints

Joints measuring exactly 1/8 inch sit on the decision point:

• For floors with standard tiles: Use sanded grout to prevent shrinkage
• For walls or polished tile: Use unsanded to avoid scratching
• For rectified tiles (perfectly uniform edges): Either type works

Comparison Table

Factor	Sanded Grout	Unsanded Grout
Joint width	1/8” to 1/2”	Up to 1/8”
Contains sand	Yes	No
Prevents shrinkage	Excellent	Limited
Scratches polished surfaces	Yes	No
Bonds to vertical surfaces	Moderate (tends to slump)	Excellent
Durability under foot traffic	Excellent	Good
Application ease	Easy	Requires more skill
Typical use	Floors, large tiles	Walls, glass tile, marble

How Tile Size Affects Grout Consumption

Tile size dramatically impacts grout usage. The relationship is exponential, not linear.

Large Format Tiles (12×12 and bigger)

12×12 inch tiles:

• One tile covers 1 square foot
• Minimal grout lines per square foot
• 10 lb bag covers 60–75 sq ft with 1/8” joints

12×24 inch tiles:

• One tile covers 2 square feet
• Even fewer grout lines
• 10 lb bag covers 75–100 sq ft with 1/8” joints
• Modern, sleek appearance
• Hides fewer installation imperfections

24×24 inch tiles:

• One tile covers 4 square feet
• Extremely minimal grout consumption
• 10 lb bag covers 100–150 sq ft with 1/8” joints
• Requires very flat substrate
• Any lippage (uneven tile edges) is obvious

Medium Tiles (6×6 to 8×8)

6×6 inch tiles:

• Four tiles per square foot
• Double the grout lines of 12×12 tiles
• 10 lb bag covers 40–55 sq ft with 1/8” joints
• Good balance of coverage and design flexibility

8×8 inch tiles:

• 2.25 tiles per square foot
• 10 lb bag covers 50–65 sq ft with 1/8” joints
• Popular for retro and vintage looks

Small Format and Mosaic (under 4×4)

4×4 inch tiles:

• 9 tiles per square foot
• Triple the grout lines of 12×12 tiles
• 10 lb bag covers 30–40 sq ft with 1/8” joints
• Vintage aesthetic with significant grout maintenance

2×2 inch and smaller (mosaic):

• 36+ tiles per square foot
• Massive grout consumption
• 10 lb bag covers 15–25 sq ft with 1/16” joints
• Usually sold as mesh-backed sheets
• Requires 15–20% waste factor due to cutting

Why mosaic uses so much grout: A 12×12 inch tile has 48 inches of grout perimeter. Nine 4×4 inch tiles covering the same area have 144 inches of perimeter—triple the grout. The relationship is inverse and exponential.

Joint Width Guidelines by Application

Joint width affects appearance, maintenance, and grout consumption.

1/16 Inch Joints

Best for:

• Large-format rectified tiles (edges cut precisely)
• Modern, minimalist designs
• Polished porcelain slabs

Challenges:

• Requires perfectly sized tiles (tolerance ±0.5mm)
• Any size variation creates lippage
• Difficult to fill completely without voids
• Professional installation recommended

Grout consumption: Minimal, but precise application required.

1/8 Inch Joints

Best for:

• Standard residential floor and wall tile
• Quality ceramic and porcelain tiles
• Most bathroom and kitchen applications

Benefits:

• Accommodates slight tile size variations (±1mm)
• Easier installation than 1/16” joints
• Still creates clean, modern appearance
• Standard recommendation for most projects

Grout consumption: Baseline coverage rates apply.

1/4 Inch Joints

Best for:

• Standard construction-grade tiles with size variation
• DIY installations needing error forgiveness
• Rustic and traditional designs
• Handmade or artisan tiles

Benefits:

• Forgives tile size irregularities
• Easier for inexperienced installers
• Hides minor installation imperfections
• Creates traditional grout-line appearance

Grout consumption: Approximately double 1/8” joints.

3/8 to 1/2 Inch Joints

Best for:

• Terracotta and Saltillo tile
• Handmade tiles with significant size variation
• Rustic, farmhouse, and Mediterranean styles

Challenges:

• High grout consumption (triple 1/8” joints)
• Longer curing time due to volume
• More surface area to clean and maintain
• Requires careful packing to avoid voids

Grout consumption: 3× standard coverage, requires sanded grout.

How Joint Depth Affects Grout Volume

Joint depth is the thickness of the tile. Most grout fills the full depth, but some applications vary.

Standard Depth (match tile thickness)

Typical tile thickness:

• Ceramic floor tile: 1/4 to 3/8 inch
• Porcelain floor tile: 3/8 to 1/2 inch
• Ceramic wall tile: 1/4 inch
• Glass tile: 1/4 inch

Fill joints to the full depth for complete seal and proper tile support.

Shallow Fill Applications

Some installers fill only the top 1/2 to 2/3 of joint depth to save grout. This is acceptable only when:

• Thinset already fills joint at tile bottom
• Tiles are firmly supported by thinset
• Water penetration is not a concern

Shallow filling reduces grout consumption by 30–50% but creates risk of water infiltration if thinset doesn’t completely fill joint bottoms.

Deep Fill Applications

When installing tile over radiant heat cables or in shower pans, joint depth may exceed tile thickness. Calculate grout volume based on actual joint depth, which can be 1/2 to 3/4 inch in these applications.

Grout Coverage Calculation Examples

Example 1: Standard Bathroom Floor

Scenario: 5×8 ft bathroom (40 sq ft), 12×12 inch ceramic tile, 1/8 inch joints

Calculation:

• Tile area: 12 × 12 = 144 sq in
• Tile plus joint: 12.125 × 12.125 = 147.02 sq in
• Grout ratio: 1 - (144 ÷ 147.02) = 0.0205 (2.05%)
• Floor area: 40 sq ft × 144 = 5,760 sq in
• Grout surface: 5,760 × 0.0205 = 118 sq in
• Joint depth: 0.25 inch (1/4 inch tile)
• Grout volume: 118 × 0.25 = 29.5 cubic inches

Coverage: One 10 lb bag covers 60–75 sq ft with these specs = 1 bag needed, but buy 2 bags for safety margin and future repairs.

Example 2: Kitchen Backsplash

Scenario: 4×8 ft backsplash (32 sq ft), 3×6 inch subway tile, 1/8 inch joints

Calculation:

• Tile area: 3 × 6 = 18 sq in
• Tile plus joint: 3.125 × 6.125 = 19.14 sq in
• Grout ratio: 1 - (18 ÷ 19.14) = 0.0596 (5.96%)
• Wall area: 32 sq ft × 144 = 4,608 sq in
• Grout surface: 4,608 × 0.0596 = 274.6 sq in
• Joint depth: 0.25 inch
• Grout volume: 274.6 × 0.25 = 68.6 cubic inches

Coverage: One 10 lb bag covers 45–60 sq ft with subway tile = 1 bag needed.

Example 3: Shower Floor

Scenario: 3×4 ft shower pan (12 sq ft), 2×2 inch mosaic on mesh sheets, 1/16 inch joints

Calculation:

• Tile area: 2 × 2 = 4 sq in
• Tile plus joint: 2.0625 × 2.0625 = 4.25 sq in
• Grout ratio: 1 - (4 ÷ 4.25) = 0.0588 (5.88%)
• Floor area: 12 sq ft × 144 = 1,728 sq in
• Grout surface: 1,728 × 0.0588 = 101.6 sq in
• Joint depth: 0.25 inch
• Grout volume: 101.6 × 0.25 = 25.4 cubic inches

Coverage: One 10 lb bag covers 20–30 sq ft with mosaic = 1 bag needed (unsanded grout).

Mixing and Application Best Practices

Buying the correct amount prevents shortages. Proper application prevents failures.

Mixing Grout Correctly

The water ratio rule:

• Add grout powder to water, never water to powder
• Pour 75% of recommended water into bucket first
• Add powder while mixing with drill and paddle
• Add remaining water gradually to reach peanut butter consistency

The slaking period:

1. Mix for 2–3 minutes until smooth
2. Let rest (slake) for 10 minutes
3. Remix for 1 minute without adding water
4. Use within 30–45 minutes

Critical mistake: Adding water after slaking weakens grout and causes excessive shrinkage. If grout stiffens during application, discard it and mix a new batch.

Application Technique

Tools needed:

• Rubber grout float
• Large grout sponge
• Bucket of clean water
• Grout bag (for wide or deep joints)

Application steps:

1. Ensure tiles are set: Wait 24–72 hours after tile installation for thinset to cure
2. Remove spacers: Pull all tile spacers from joints
3. Apply grout: Hold float at 45° angle, work diagonally across tiles
4. Pack joints: Make two passes to ensure complete filling without voids
5. Remove excess: Scrape float across tiles at 90° angle
6. Wait 15–30 minutes: Let grout firm up but not harden
7. Clean tiles: Use damp (not wet) sponge in circular motions
8. Rinse sponge frequently: Change water when it gets cloudy
9. Final wipe: After 1–2 hours, remove grout haze with dry cloth

Working Time Considerations

Standard conditions (70°F, 50% humidity):

• Working time: 30–45 minutes
• Cleanup window: 15–30 minutes after application
• Foot traffic: 24 hours minimum
• Full cure: 72 hours before sealing

Hot weather (>85°F):

• Working time: 20–30 minutes
• Grout dries faster on tile surfaces
• Mix smaller batches
• Keep grout covered between applications

Cold weather (<50°F):

• Working time: 45–60 minutes
• Slower curing requires longer wait before sealing
• May need 5–7 days before sealing

Curing and Sealing

Curing Process

Grout gains strength through hydration, not evaporation. Proper curing requires:

First 24 hours:

• No foot traffic
• No water exposure
• Maintain room temperature above 50°F
• Avoid drafts that dry grout too quickly

Days 2–3:

• Light foot traffic acceptable
• No heavy furniture or loads
• Continue to avoid water exposure
• In humid climates, run dehumidifier

Day 3–7:

• Full cure achieved (cement-based grout)
• Ready for sealing
• Safe for normal use

Common curing mistakes:

• Sealing too early (traps moisture, prevents hardening)
• Exposing to water before full cure (weakens grout)
• Extreme temperature swings during cure (causes cracks)

Sealing Grout

Why seal cement-based grout:

• Cement is porous and absorbs water, stains, oils
• Unsealed grout darkens, stains permanently
• Moisture penetration causes mold and mildew
• Sealer repels liquids while allowing vapor transmission

Sealing process:

1. Wait for full cure: Minimum 72 hours, longer in humid conditions
2. Clean thoroughly: Remove all grout haze, dirt, residue
3. Apply penetrating sealer: Use brush or applicator bottle
4. Wipe excess: Sealer should penetrate, not sit on surface
5. Apply second coat: After first coat dries (typically 1–2 hours)
6. Cure sealer: Wait 24 hours before water exposure

Resealing schedule:

• High-traffic floors: Annually
• Showers and wet areas: Every 1–2 years
• Standard floors: Every 2–3 years
• Walls: Every 3–5 years

Sealer types:

• Penetrating sealer: Soaks into grout, invisible finish
• Membrane-forming sealer: Creates surface coating, may yellow
• Color sealer: Changes grout color while sealing
• Grout release: Applied before grouting to ease cleanup

Epoxy grout note: Epoxy grout is non-porous and doesn’t require sealing. It costs 3–5× more but eliminates sealing maintenance.

Common Mistakes to Avoid

1. Underestimating Grout Consumption

Mistake: Calculating for 100 sq ft floor, buying exactly 2 bags, then running out at 90 sq ft because tiles had deep beveled edges that consumed extra grout.

Fix: Always buy one extra bag beyond calculation. Grout is inexpensive ($10–15 per bag). Running short costs far more in time, frustration, and color mismatch than the cost of one spare bag.

2. Using Old or Moisture-Contaminated Grout

Mistake: Finding a half-used bag in the garage from last year’s project. Powder has lumps from moisture absorption. Mixing it produces weak, inconsistent grout.

Fix: Store unopened grout bags in airtight plastic bins with desiccant packs. Inspect bags before use—if powder has any lumps or hard chunks, discard it. Grout costs $10 per bag. Foundation repairs from grout failure cost $1,000+.

3. Mixing Too Much Grout at Once

Mistake: Mixing entire 10 lb bag at once to “save time.” Grout starts setting after 30 minutes. Last quarter of bucket is too stiff to work properly, gets thrown away.

Fix: Mix only what you can apply in 20–30 minutes. For most DIYers, this is 2–4 lbs at a time. Experienced installers can handle full bags, but they work fast.

4. Adding Water to Stiffening Grout

Mistake: Grout in bucket starts to thicken after 30 minutes. Adding more water to make it workable again.

Fix: Once grout begins to set, chemical curing has started. Adding water interrupts this process, creating weak grout that will crack and crumble. Discard stiffened grout and mix a fresh batch.

5. Grouting Before Thinset Cures

Mistake: Installing tile on Saturday, grouting Sunday morning. Thinset hasn’t cured fully. Walking on tiles to grout causes movement that breaks thinset bond.

Fix: Wait minimum 24 hours for standard thinset, 48–72 hours for rapid-set thinset. Check manufacturer specifications. Rushing this step ruins the entire installation.

6. Using Sanded Grout on Polished Marble

Mistake: Installing marble tile with 1/8” joints, using sanded grout because joint width says “use sanded.” Sand particles scratch polished marble surface during application.

Fix: For polished stone, glass tile, or metal tile, use unsanded grout even if joints are at the 1/8” borderline. Accept slightly higher shrinkage risk to avoid permanent scratching.

7. Incorrect Joint Width for Grout Type

Mistake: Using unsanded grout in 1/4” joints because it looks smoother. Grout shrinks during curing, creating gaps that leak water.

Fix: Follow the 1/8” rule religiously. Joints ≥1/8” require sanded grout. No exceptions for aesthetic preferences.

Pro Tips from Professional Tile Setters

1. Buy One Bag Per Room Extra

Beyond the calculated amount, buy one spare bag per room. For a 100 sq ft bathroom needing 2 bags, buy 3. For a kitchen needing 4 bags, buy 5. The spare bag serves three purposes:

• Buffer for calculation errors in grout consumption
• Repair stock for fixing cracks or damage over next 5–10 years
• Color matching for future repairs (grout color varies between batches)

Store the unopened bag in a closet (climate-controlled space, not garage). Label it with room name and install date.

2. Test Grout Color Before Full Application

Grout color when dry differs from wet color. Some grouts darken significantly, others lighten.

Testing procedure:

1. Mix small amount (1 cup) of grout
2. Fill joints on sample board or inconspicuous corner
3. Let cure fully (72 hours)
4. Evaluate color match with tiles
5. Adjust grout color choice if needed before grouting entire floor

This costs 20 minutes and one cup of grout. It prevents $500+ mistakes when grout color clashes with tile.

3. Use Grout Release on Porous Tile

Rough-textured tile (natural stone, unglazed ceramic, terracotta) absorbs grout into surface pores. Cleaning it off is nearly impossible without grout release.

Application:

1. Apply grout release to tile surfaces before grouting
2. Let dry per manufacturer specifications
3. Grout normally
4. Cleanup is 10× easier

Grout release costs $20–30 per quart. It saves hours of cleanup labor on textured tile.

4. Pack Joints Firmly on First Pass

Voids in grout joints cause two problems:

• Water penetrates through voids, damaging substrate
• Thin spots crack under foot traffic pressure

Proper packing technique:

• Hold float at 45° angle
• Apply significant pressure while dragging across joints
• Work in multiple directions (horizontal, vertical, diagonal)
• Look for air bubbles and fill them
• Make second pass at 90° to remove excess

Well-packed joints last 15–20 years. Loosely filled joints fail in 2–5 years.

5. Change Sponge Water Frequently

Dirty sponge water re-deposits grout haze on tiles, creating a film that requires acid washing to remove.

Water changing schedule:

• After every 20–30 sq ft grouted
• When water turns milky or cloudy
• If you see grout residue on sponge after rinsing

Use two buckets: one for initial wipe, one for final rinse. This keeps final rinse water cleaner longer.

6. Avoid Grout on Expansion Joints

Tile installations need expansion joints at these locations:

• Where tile meets different materials (wood, carpet, metal)
• Inside corners (wall to wall, wall to floor)
• Perimeter edges against walls
• Every 20–25 feet in large tiled areas

Use flexible caulk (not grout) in these locations. Grout is rigid and cracks when tile expands and contracts with temperature and humidity. Caulk flexes with movement.

Match caulk color to grout color for a consistent appearance.

Frequently Asked Questions

How much grout do I need for a 100 square foot floor?

For 100 square feet with 12×12 inch tiles and 1/8 inch joints, you need 1–2 bags of 10 lb grout (buy 2 bags for safety). Smaller tiles require more grout: 6×6 inch tiles need 2–3 bags, while 4×4 inch tiles need 3–4 bags for the same floor area. Joint width also affects consumption—1/4 inch joints use approximately double the grout of 1/8 inch joints. Always buy one extra bag beyond calculations as a safety margin and future repair stock.

What’s the difference between sanded and unsanded grout?

Sanded grout contains fine sand particles and is required for joints 1/8 inch and wider because sand prevents shrinkage in wide gaps. Unsanded grout is smooth cement without sand, used for joints under 1/8 inch and on polished surfaces where sand would cause scratching (marble, glass tile, metal tile). The 1/8 inch threshold is critical—using unsanded in wide joints causes shrinkage cracks, while using sanded on polished surfaces creates permanent scratches during application.

How do I calculate grout for irregularly shaped rooms?

Break irregular shapes into rectangles, calculate each section separately, then add the totals together. For L-shaped rooms, measure the long section and short section as two rectangles. For curved areas or complex shapes, use the largest rectangle that fits within the space and add 15–20% extra. Grout is inexpensive enough that slight overestimation is smarter than running short. Alternatively, trace the room outline on graph paper at scale, count the squares, and convert to square footage.

Can I use leftover grout from a previous project?

Only if the grout bag remained sealed and was stored in a dry, climate-controlled location. Grout powder absorbs moisture from air, causing it to harden in the bag even when “sealed.” Check powder consistency—if you find any lumps or hard chunks, discard the bag. Compromised grout never achieves full strength and will crack within 1–2 years. At $10–15 per bag, buying fresh grout is cheaper than repairing failed grout lines. Store unused grout in airtight plastic containers with desiccant packs for maximum shelf life.

How long does grout last before I need to regrout?

Properly installed and sealed grout lasts 15–20 years in residential applications. Signs you need to regrout include crumbling or missing grout, persistent staining that deep cleaning can’t remove, cracks wider than hairline thickness, water leaking through grout lines, or mold growth that reappears after cleaning. Surface discoloration alone doesn’t require complete regrout—try deep cleaning with alkaline cleaner and grout brush first, then apply grout colorant if staining persists. Grout colorant seals and colors simultaneously, often eliminating the need to remove and replace grout.

Should I seal grout immediately after grouting?

No. Wait minimum 72 hours for cement-based grout to cure fully before sealing. Sealing too early traps moisture inside grout, preventing proper hardening and creating chalky, weak grout that crumbles under pressure. In humid climates or cool temperatures, wait 5–7 days. Test cure by placing plastic wrap over grout overnight—if moisture condenses on underside of plastic in the morning, grout hasn’t cured fully. Once cured, apply penetrating sealer to protect against stains and moisture while allowing grout to breathe.

Use our grout calculator to calculate exact grout quantities for your tile project with automatic recommendations for sanded or unsanded grout based on joint width.