Grout Calculator
Estimate the grout for a tile job from the joint volume — the space between the tiles. Enter the area, tile size, joint width, and depth to get the volume, plus a rough weight and bag count to sanity-check against your product.
Joint depth is usually close to the tile thickness (often 1/4–3/8 in for floor tile).
Advanced: weight & bag estimate
A typical placed cementitious grout is around 100–125 lb/ft³. Adjust to match your product if you can.
Read the bag weight off your grout — 10 lb and 25 lb are common.
Formula & how it works
For each tile-plus-joint cell, the grout fraction is joint × (tile L + tile W + joint) ÷ ((tile L + joint) × (tile W + joint)). Multiply by the joint depth and the area to get the joint volume.
Volume = area × 144 × (that fraction × depth) in cubic inches, then converted to cubic feet. Estimated weight = volume × density; bags = weight ÷ bag size, rounded up.
Worked example
A 10 × 10 ft floor (100 ft²) with 12 × 12 in tiles, a 1/8 in joint, and 1/4 in depth needs about 74 in³ of grout — roughly 0.043 ft³. With 10% waste and a density of 110 lb/ft³ that's about 5 lb, so a single 25 lb bag more than covers it. Drop to 2 × 2 in mosaic and the same floor jumps past 400 in³ — several times the grout.
Estimating grout well
The joint volume is the honest number
The one thing that's pure geometry here is the volume of the joints — it follows directly from tile size, joint width, joint depth, and area. Everything downstream (weight, bags) depends on the specific grout, so treat those as ballpark figures. If you want a firm purchase count, take the volume and area from here and match them to the coverage chart printed on your bag.
Tile size drives everything
Grout lives in the joints, and small tiles simply have more joint per square foot. Going from 12-inch tiles to 2-inch mosaic on the same floor can multiply the grout several times over. Large-format tiles with tight joints, at the other end, barely use any. Wider and deeper joints add grout too, in direct proportion.
Buy a little extra
Running out partway through means mixing a fresh batch, and a second batch can cure a shade off from the first. One spare bag is cheap next to re-grouting a mismatched floor, so round up rather than cutting it fine.