Thinset Calculator
Enter the area you're tiling and the trowel notch you'll use — coverage per bag falls fast as the tile (and trowel) gets bigger. You'll get the bags of thinset mortar to buy. Get the area from the tile calculator, then size the thinset here.
Results
How the thinset calculator works
Thinset — the cement-based mortar that bonds tile to the floor or wall — is estimated by coverage per bag, and that coverage is set almost entirely by the trowel notch you use. Bigger tile needs a deeper notch to get full contact, and a deeper notch lays a thicker bed, so a 50 lb bag that covers about 85 sq ft under small tile drops to around 45 sq ft under large-format tile.
Formula: area × (1 + overage%) ÷ coverage per bag = bags (rounded up)
| Tile / notch | Coverage |
|---|---|
| Mosaic & small — 3/16" V-notch | ≈ 95 sq ft |
| Up to 12" — 1/4" square notch | ≈ 85 sq ft |
| 12–16" — 1/4" × 3/8" notch | ≈ 60 sq ft |
| 16"+ large format — 1/2" square notch | ≈ 45 sq ft |
| Extra-large / uneven — 3/4" U-notch | ≈ 30 sq ft |
These are typical figures — the coverage printed on your bag is the number to trust, since it varies by brand and by whether the thinset is modified or unmodified. A 40 lb bag covers about four-fifths of what a 50 lb bag does.
Thinset tips before you buy
- Match the trowel to the tile: too small a notch starves the bond, too large squeezes mortar up into the grout joints and wastes material.
- Back-butter large-format and natural-stone tile — spread a thin coat on the back of each tile as well as the floor — to hit the 80–95% coverage those tiles need. That uses more thinset, so lean toward the higher overage.
- Only mix what you can use in about 30–40 minutes; thinset that has started to cure can't be re-tempered with more water.
- Use the right type: unmodified thinset under most porcelain and stone, modified for large tile and over membranes — check the tile and membrane instructions.
- This calculator sizes the setting mortar only. Grout for the joints and any waterproofing membrane are separate line items.
Frequently asked questions
How much thinset do I need for 100 square feet of tile?
For standard tile up to 12 inches with a 1/4-inch square-notch trowel, a 50 lb bag covers about 85 sq ft. With a 10% overage, 100 sq ft needs about 110 sq ft of coverage — that's 2 bags.
How many square feet does a bag of thinset cover?
A 50 lb bag covers roughly 85–95 sq ft under small tile with a 1/4-inch notch, but only about 45 sq ft under large-format tile with a 1/2-inch notch, and around 30 sq ft with a 3/4-inch U-notch. Coverage falls as the trowel notch grows.
How do I calculate thinset for large format tile?
Large tile needs a deeper trowel notch — usually 1/2 inch — which cuts a 50 lb bag to about 45 sq ft. Divide your area (plus overage) by that figure and round up, and plan to back-butter each tile, which uses a little more.
Is thinset the same as grout?
No. Thinset is the mortar under the tile that bonds it to the surface; grout fills the joints between tiles afterward. They're bought and estimated separately — this calculator sizes the thinset only.