Tile Grout Calculator (Pounds and Bags of Grout)
How much grout a tile job takes from the tile size, joint width, joint depth and area, in pounds and bags. The grout density is editable so you can match your product.
Formula
Each tile plus its joint is a (L + J) × (W + J) module, of which J × (L + W + J) is joint. Joint share = J(L + W + J) ÷ ((L + J)(W + J)). Grout volume (cu ft) = area × joint share × depth(in) ÷ 12; pounds = volume × density × (1 + waste); bags = ⌈pounds ÷ bag size⌉.
Worked example
Inputs: Tiled area = 100 sq ft; Tile length = 12 in; Tile width = 12 in; Joint width (1/8 in = 0.125) = 0.125 in; Joint depth (usually tile thickness) = 0.375 in; Grout weight per cubic foot of joint (from your grout data sheet; ~100 sanded, ~85 unsanded) = 100 lb/cu ft; Waste allowance = 10 %; Bag size = 25 lb.
| Joint share of surface pct | 2.05 |
|---|---|
| Grout cubic inches | 110.8 |
| Grout lb | 6.41 |
| Grout lb with waste | 7.05 |
| Bags | 1 |
FAQ
How much grout for 100 sq ft of 12 × 12 tile?
With a 1/8 in joint, 3/8 in deep, the joints are 2.05% of the surface: 100 × 0.0205 × 0.375 ÷ 12 = 0.064 cu ft, about 6.4 lb of sanded grout, 7.1 lb with 10% waste. One 25 lb bag is plenty. Merkrete's calculator gives about 6.5 lb for the same job.
Why do small tiles take so much more grout?
Joint length per square foot goes up as tiles get smaller. 3 × 6 subway tile with a 1/16 in joint has about 3.05% of its surface in joints, versus 2.05% for 12 × 12 tile with a joint twice as wide.
What joint depth do I use?
The tile thickness, since grout fills the joint from the setting bed to the tile face. Measure one of your tiles with a ruler or caliper.
Sanded or unsanded?
Follow your tile and grout maker: the grout bag lists the joint widths it is made for. Then set the density to match that product.
What density should I use?
Use your grout's data sheet or coverage chart. The factors in Merkrete's calculator work out to about 100 lb per cubic foot for sanded, 85 for non-sanded and 89 for epoxy, so those are reasonable starting points.
Sources
- Merkrete (Parex USA) grout calculator: joint-volume formula and grout-type factors (75 for sanded, 64 for non-sanded, 67 for epoxy, which work out to about 100, 85 and 89 lb per cubic foot of joint)
- Geometry (volume/area formulas); no external constant needed
Related
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Last reviewed 2026-10-20.