Grout calculator

Enter the tile, the joint and the area, and this returns the weight of grout to buy. Joint width moves the answer more than anything else here: the same floor in quarter-inch joints needs about twice what it needs in eighth-inch ones.

Nothing you type here is sent anywhere. The arithmetic runs on your device and the page makes no network request — see the privacy note. The bag's own coverage chart overrides this page; see the terms of use.

The formula, in full

One tile plus its share of the joints occupies a rectangle of (length + joint) by (width + joint). The tile itself is length by width, and the difference between the two is grout. That difference, divided by the whole rectangle, is the fraction of the surface that is joint.

Multiply that fraction by 144 square inches and by the tile thickness, and you have the cubic inches of grout in one square foot. Multiply by the area, divide by 1,728 to reach cubic feet, and multiply by the density of the dry mix.

Worked through for a 12-by-12-inch tile with 1/8-inch joints at 3/8-inch thickness: the cell is 12.125 by 12.125 inches, or 147.0 square inches, of which the tile is 144, so joints are 3.0 square inches — 2.05 percent of the surface. That is 1.11 cubic inches of grout per square foot, and 100 square feet comes to about 6.7 pounds.

The one number we assume

Density. Everything above is geometry and holds regardless of brand, but turning cubic feet into pounds needs the density of the dry mix, and this page uses 105 pounds per cubic foot as a working figure rather than a published one. Products differ, sanded and unsanded differ, and the coverage chart printed on your bag is the authority.

What that means in practice: treat this as the number that tells you whether to buy one bag or four, then check the bag. The geometry will not change; the pounds may move by a tenth either way.

Why tile size changes everything

A square foot of 12-inch tile contains about two linear feet of joint. The same square foot in 24-by-48-inch tile contains about three quarters of a foot. Grout quantity follows joint length, so moving to large format cuts grout by two thirds — and moving to subway or mosaic multiplies it: the 3-by-6-inch row above needs three times what 12-inch tile needs over the same area.

This is why mosaic sheets and penny rounds surprise people at the counter. The tile is small, the area looks modest, and the grout is the largest material line in the job.

The rest of the tiling job

Grout is the last material and the cheapest. The tile itself is counted by the tile calculator, including the waste factor that the layout decides, and what the finished job costs — where labor runs $3 to $15 per square foot against tile at $2 to $15 — is in what tile installation costs.

In a bathroom, grout and tile sit inside a larger budget dominated by plumbing and waterproofing: what a bathroom remodel costs lays out that split, and a shower on its own is priced separately because the enclosure, not the tile, decides it.