Construction
Grout Calculator
Running out of grout 80% of the way through a backsplash means buying another bag, mixing a fresh batch, and dealing with a visible color shift between batches — grout dries differently from different mixes. Buying way too much wastes $20-40 a bag plus opened bags don't shelf-store well. This calculator gives you a real pound count and bag count based on the actual variables that drive grout consumption: tile size (smaller tiles use more), joint width (wider joints use more), tile thickness (thicker = more grout depth per joint), and total tile area. Works for floor tile, wall tile, mosaic, subway, and large-format.
Grout (lb)
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- 25 lb bags
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- 10 lb bags
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Why tile size and joint width matter so much
Grout fills the channels between tiles. Smaller tiles = more channels per square foot = more grout. A square foot of 1" mosaic has roughly 6x as much joint length as a square foot of 12" floor tile. So a 12x12 ceramic floor at 1/8" joints uses about 1/8 lb per sq ft, while a glass mosaic backsplash with 1/16" joints uses about 1/4 to 1/2 lb per sq ft.
The formula behind the calculator: grout volume per sq ft = (joint width × tile thickness × 12) ÷ tile size, then multiply by a density factor (~0.6 lb per cubic inch for mixed sanded grout).
Worked example: 100 sq ft of 12" porcelain floor tile, 3/8" thick, with 1/8" joints. Per-sq-ft grout = (0.125 x 0.375 x 12) ÷ 12 x 0.6 = ~0.028 cubic inches per sq ft... no wait, the math works out to about 12 lb total grout for the whole 100 sq ft, or 1 bag of 25-lb grout with comfortable leftover. Buy 1 bag of sanded grout; you'll use about half.
Sanded vs. unsanded vs. epoxy
- Unsanded: for joints under 1/8" — polished marble, glass tile, narrow-joint mosaics. Smooth texture, won't scratch polished stone.
- Sanded: for joints 1/8" to 3/8" — the standard for most floor and wall tile. The sand prevents shrinkage cracks in wider joints.
- Epoxy grout: chemically waterproof, stain-proof, no sealing required. 3-5x the cost of cement grout. Worth it in showers, kitchen backsplashes, and any high-stain area. Trickier to install — has a short open time before it sets up hard.
- Pre-mixed urethane grout: like epoxy in performance, easier to install (no mixing). Premium price but DIY-friendly.
How to use this calculator
- Total tile area: square feet of tile, not square feet of room. For a backsplash, just measure the actual backsplash area.
- Tile size: the nominal size in inches. For rectangular tile (subway, plank), use the smaller dimension — it dominates the joint count.
- Joint width: 1/16" (0.0625) for glass and stone, 1/8" (0.125) for most ceramic, 3/16" (0.1875) for handmade or rustic tile, 1/4" (0.25) for slate and quarry tile.
- Tile thickness: 1/4" for mosaic, 3/8" for typical floor tile, 1/2" for natural stone, 3/4" for porcelain pavers.
- The calculator returns total pounds of grout plus the bag count in standard 25-lb and 10-lb sizes.
Common scenarios
30 sq ft subway tile backsplash, 3x6 tiles, 1/16" joints. ~3 lb of unsanded grout. One 10-lb bag is plenty (most goes unused). Pick the color carefully — it's the most visible variable on a backsplash.
200 sq ft kitchen floor, 18" porcelain, 1/8" joints. ~15 lb of sanded grout. One 25-lb bag covers it with leftovers. Use a high-performance epoxy or urethane grout for kitchens — cement grout stains within a year from spilled wine, coffee, and grease.
120 sq ft shower walls, 1"x1" glass mosaic, 1/16" joints. ~35 lb of unsanded epoxy grout. Plan two 20-lb units of epoxy plus a backup unit. Mosaics chew through grout fast because of the joint count.