LayoutWise

Thinset Calculator

Enter the area and tile size. You get the trowel notch the tile needs and how many bags of thinset to buy, with an allowance for back-buttering.

Your tile

1. Area
2. Tile & trowel

Bags

4

50 lb each

Thinset

196 lb

89 kg

Trowel

1/2"

square-notch

Coverage

42 sq ft

per 50 lb bag

⚠ Tile 15" or longer: use a mortar labeled for large and heavy tile (LHT), and back-butter each tile for full coverage.

Trowel notch

1/2" x 1/2" square-notch

Bigger tile needs deeper ridges so the mortar can fill the gap once the tile is pressed down. Lift a tile now and then: you want 80% or more of the back covered (95% in showers and outdoors).

Shopping list

  • ✓50 lb bags of large-and-heavy-tile (LHT) thinset: 4 (196 lb)
  • ✓Trowel: 1/2" x 1/2" square-notch
  • ✓Margin trowel, mixing paddle and a 5-gallon bucket

Coverage per bag varies by brand — check the trowel chart on the bag. Need tile and grout counts too? Use the tile calculator.

How much thinset do I need?

Thinset coverage depends almost entirely on the trowel notch: the deeper the ridges, the more mortar per square foot. A 50 lb bag typically covers about 95 sq ft with a 3/16" V-notch, 85 sq ft with a 1/4" square-notch, 60 sq ft with a 1/4" x 3/8" notch and around 40 sq ft with a 1/2" notch. Brands differ, so check the chart on your bag.

Example: 120 sq ft of 12" x 24" tile calls for a 1/2" square-notch trowel. With 10% extra and 25% for back-buttering that's about 196 lb — four 50 lb bags.

Which trowel for which tile?

Longest tile sideTypical trowel
Mosaics under 4"3/16" V-notch
4" to 12"1/4" x 1/4" square-notch
Over 12" up to 18"1/4" x 3/8" square-notch
18" and larger1/2" x 1/2" square-notch

The real test is coverage, not the notch size. Industry standards call for at least 80% mortar contact on floors in dry areas and 95% in showers and outdoors. Pull up a tile right after setting it and look at the back.

Large tile and back-buttering

Tile with any side 15" or longer is called large-format. It needs a mortar rated for large and heavy tile, and a thin coat spread on the back of each tile (back-buttering) to fill the hollows. Budget about a quarter more mortar for it.

Planning the whole floor? The tile calculator lays out the tiles and counts tile, thinset and grout. For grout alone, use the grout calculator.