About This Tool
Grout fills the gaps between tiles, locking them in place and preventing moisture infiltration that causes mold and tile failure. Running out of grout mid-project creates visible seam lines where you mix a new batch, ruining the uniform appearance. Buying too much wastes money because opened grout bags absorb moisture and harden into unusable chunks. This grout calculator eliminates guesswork by calculating exact grout volume based on tile size, joint width, joint depth, and total area, then converting that volume to bag quantities for both 10 lb and 25 lb sizes. Grout coverage varies dramatically based on tile size and joint width. Small mosaic tiles create hundreds of linear feet of grout lines per square foot, consuming far more grout than large-format tiles. A 1-inch mosaic with 1/16-inch joints requires triple the grout of a 12x12-inch tile with 1/4-inch joints covering the same floor area. Joint width matters even more. Doubling joint width from 1/8 inch to 1/4 inch roughly doubles grout consumption. Our calculator accounts for these variables using the industry-standard formula that professional installers rely on. Grout type selection depends entirely on joint width. Joints 1/8 inch and wider require sanded grout, which contains fine sand particles that prevent shrinkage and cracking in wide gaps. Joints under 1/8 inch need unsanded grout because sand particles can scratch polished marble, glass tile, or other delicate surfaces. The calculator automatically recommends sanded or unsanded based on your joint width input, ensuring you purchase the correct product for a professional-looking installation.
Understanding the Grout Calculation Formula
Grout volume calculation starts with determining how much of your floor area is grout joints versus tile surface:
The Formula:
Grout Area Ratio = 1 - (Tile Length × Tile Width) / ((Tile Length + Joint Width) × (Tile Width + Joint Width))
This ratio tells you what percentage of your floor is grout. Multiply by total area and joint depth to get grout volume.
Example Calculation:
For a 100 sq ft floor with 12×12 inch tiles and 1/4 inch joints at 1/4 inch depth:
- Tile area: 12 × 12 = 144 square inches
- Tile plus joint area: (12 + 0.25) × (12 + 0.25) = 12.25 × 12.25 = 150.06 square inches
- Grout ratio: 1 - (144 / 150.06) = 1 - 0.9596 = 0.0404 (4.04% of floor is grout)
- Total area in square inches: 100 sq ft × 144 = 14,400 sq in
- Grout area: 14,400 × 0.0404 = 581.76 sq in of grout surface
- Grout volume: 581.76 sq in × 0.25 inch depth = 145.44 cubic inches = 0.084 cubic feet
A 10 lb bag of grout typically covers 50-75 square feet with standard 12×12 tiles and 1/8 inch joints. Smaller tiles or wider joints drastically reduce coverage because more of the floor is grout joints. Our calculator adjusts the base coverage rate based on your specific tile size and joint width to provide accurate bag estimates.
Why Manual Estimates Fail:
Many DIYers guess based on floor area alone, ignoring tile size and joint width. A 100 sq ft bathroom with 2-inch mosaic tiles needs 3-4 times more grout than the same bathroom with 12-inch tiles. The formula accounts for the exponential increase in grout lines as tile size decreases and joint width increases.
Sanded vs Unsanded Grout: When to Use Each
Grout type selection is not optional. Using the wrong type causes installation failure:
Sanded Grout (for joints 1/8" and wider):
Contains fine silica sand mixed with cement. The sand acts as aggregate, preventing shrinkage in wide joints. Without sand, grout shrinks as it cures, creating gaps that allow water penetration and tile movement. Sanded grout is harder and more durable for floor applications where foot traffic causes wear. Use on ceramic tile, porcelain tile, natural stone (non-polished), and any joint wider than 1/8 inch. Standard coverage is 50-75 sq ft per 10 lb bag for typical installations.
Unsanded Grout (for joints under 1/8"):
Pure cement-based grout without sand particles. Smooth texture allows it to pack tightly into narrow joints without voids. Critical for polished marble, glass tile, and metal tile where sand would scratch the surface during application. Also used for vertical applications like shower walls where sanded grout tends to slump before curing. Coverage is similar to sanded grout when applied at the same joint dimensions, but narrow joints mean you use less total grout.
The 1/8 Inch Rule:
Joints exactly 1/8 inch wide sit on the borderline. For rectified tiles with precisely uniform edges, unsanded grout works. For standard tiles with slight size variations, sanded grout prevents shrinkage cracks. When in doubt at 1/8 inch, choose sanded for floors and unsanded for walls. Grout manufacturers mark this threshold on every bag because crossing it causes problems.
Epoxy Grout (premium option):
Not cement-based. Uses epoxy resin that hardens chemically without shrinking. Nearly impervious to stains, chemicals, and moisture. Required for commercial kitchens, laboratories, and areas exposed to acids or harsh cleaners. Also ideal for shower floors and kitchen backsplashes where stain resistance matters. Costs 3-5 times more than standard grout and requires skilled application because it sets quickly and is difficult to clean off tile surfaces. Coverage is lower than cement grout, approximately 30-40 sq ft per unit, because it is thicker and harder to spread.
Color Matching:
Grout color dramatically affects tile appearance. Light grout on dark tile creates a grid pattern. Matching grout color to tile color minimizes grout lines for a monolithic look. Buy all grout from the same batch because color varies slightly between production runs. Test the color on a sample board before grouting the entire floor because grout darkens or lightens as it cures depending on humidity and application thickness.
How Joint Width Affects Grout Consumption
Joint width has a non-linear effect on grout consumption. Doubling joint width more than doubles grout usage:
1/16 inch joints: Minimum width for rectified tiles with perfectly uniform edges. Creates tight, modern look. Requires only 0.2-0.3 kg grout per square meter. Difficult to fill completely without voids. Grout float must be used at precise angles. Best left to professionals. Common on large-format porcelain slabs and polished rectified tiles. Unsanded grout only.
1/8 inch joints: Standard minimum for most tile installations. Accommodates slight size variations in tiles. Uses approximately 0.3-0.5 kg grout per square meter. The threshold between sanded and unsanded grout. Easier to fill than 1/16 inch joints but still requires careful technique. Suitable for most floor and wall applications with quality tiles.
1/4 inch joints: Industry standard for most residential tile installations. Wide enough to forgive minor tile size irregularities and installation imperfections. Uses approximately 0.5-0.7 kg grout per square meter. Sanded grout required. Easier for DIY installers to achieve complete joint filling without voids. Provides visual interest and hides imperfections better than narrow joints.
3/8 inch to 1/2 inch joints: Wide joints create bold design statements and accommodate handmade or rustic tiles with significant size variation. Consumption increases to 0.8-1.2 kg per square meter. Requires sanded grout with careful packing to avoid shrinkage voids. Takes longer to cure completely due to volume. Common with terracotta, Saltillo tile, and artisan ceramic tiles. Wider joints are easier to clean but collect more dirt over time.
Why Joint Width Matters Beyond Grout Quantity:
Narrow joints showcase tile quality and create seamless appearance but require perfectly sized tiles and expert installation. Any lippage (tile edges at different heights) becomes glaringly obvious. Wide joints are more forgiving of size variation and installation errors but create busy visual appearance and more surface area for cleaning. The joint width you choose affects grout consumption, installation difficulty, maintenance requirements, and final aesthetic.
Pro Tips for Grout Application
Buying the right amount is only half the battle. Application technique determines success:
Mixing Grout Properly:
Add grout powder to water, never water to powder. Pour 3/4 of recommended water into bucket first, add powder while mixing, then add remaining water gradually to achieve peanut butter consistency. Mix for 2-3 minutes, let slake (rest) for 10 minutes, then remix. Do NOT add more water after slaking because this weakens the grout. Over-watered grout shrinks excessively and never achieves full strength. Under-watered grout is difficult to pack into joints and leaves voids.
Working Time:
Standard grout remains workable for 30-45 minutes after mixing. Mix only what you can apply in that window. In hot weather or low humidity, grout dries faster. In cool, humid conditions, working time extends. Once grout starts to stiffen in the bucket, discard it. Do NOT add water to extend working time because this ruins the chemical cure process.
Application Technique:
Use a rubber grout float held at 45-degree angle to pack grout into joints. Work diagonally across tiles to avoid pulling grout out of joints. Make two passes: first to fill joints, second to scrape excess off tile surfaces. Clean tile surfaces with damp sponge in circular motions 15-30 minutes after application, when grout is firm but not hard. Rinse sponge frequently in clean water. Too much water during cleanup weakens surface grout. Too little water leaves grout haze on tiles.
Curing Process:
Grout reaches handling strength in 24 hours but requires 72 hours to cure fully before sealing. Avoid foot traffic for 24 hours minimum. Do NOT seal grout before it fully cures because trapped moisture prevents proper hardening. In humid climates, allow 5-7 days cure time. Run dehumidifier or fans to speed drying if necessary. Unsealed grout absorbs stains immediately, so plan sealing soon after cure is complete.
Grout Sealing:
Cement-based grout is porous and must be sealed to prevent staining and moisture absorption. Apply penetrating sealer after grout cures completely. Sealer soaks into grout and repels water and stains without changing appearance. Reapply annually in high-traffic areas, every 2-3 years elsewhere. Epoxy grout does not require sealing because it is non-porous. Test sealer on inconspicuous area first because some sealers darken grout color.
Common Mistakes to Avoid:
- Grouting before thinset fully cures (wait 24-72 hours after tile installation)
- Leaving grout haze on tiles too long (becomes nearly impossible to remove after 24 hours)
- Using dirty water during cleanup (re-deposits grout on tiles)
- Applying too much pressure during cleanup (pulls grout out of joints, creating low spots)
- Sealing grout before full cure (traps moisture, prevents hardening, causes chalky grout)
Frequently Asked Questions
How do I calculate grout for irregularly shaped areas?
Can I use the same grout for floors and walls?
How long does grout last, and when should I regrout?
What causes grout to crack, and how can I prevent it?
- Substrate movement: Tiles installed over wood subfloors or improperly prepared concrete shift slightly, cracking rigid grout. Solution: ensure subfloor is stiff enough for tile (minimum 1-1/8 inch thick plywood over 16-inch joist spacing) and use crack isolation membrane over concrete.
- Improper mixing: Too much water weakens grout and causes excessive shrinkage. Solution: follow manufacturer water ratios exactly and never add water after initial slaking period.
- Premature sealing: Sealing before grout fully cures traps moisture that prevents proper hardening. Solution: wait 72 hours minimum before sealing, longer in humid climates.
- Missing expansion joints: Large tiled areas need expansion joints every 20-25 feet to accommodate thermal expansion. Solution: install flexible caulk (not grout) at perimeter edges, inside corners, and where tile meets other materials.