Thinset Calculator

Thinset Calculator works out how many bags of tile setting mortar your job needs. Enter the area, pick the trowel notch you will actually use, say whether you are back-buttering, and read the bag count straight away. This is the mortar that goes UNDER the tile — not the grout that fills the joints afterwards. It works completely offline and nothing you enter ever leaves your phone.

HOW IT WORKS
Coverage is driven by the trowel, not by the tile:

1. It measures the area to be set from the length and width you enter.

2. Every notch size lays a known volume of mortar ridges, so each one has a published coverage in square feet per 50 lb bag: about 100 ft² for a 3/16" V-notch, 95 ft² for a 1/4" x 1/4" square notch, 63 ft² for a 1/4" x 3/8" square notch, 44 ft² for a 1/2" x 1/2" square notch and 36 ft² for a 3/4" x 9/16" U-notch. The tile size picks the notch — mosaics take the V-notch, tile up to 8 in the 1/4" square, 8 to 16 in the 1/4" x 3/8", large format the 1/2", and heavy ribbed-back tile or stone the U-notch.

3. Back-buttering — skimming a coat onto the back of the tile as well as the substrate — costs about 30 percent more mortar, so the coverage per bag drops accordingly.

4. A waste allowance you choose (typically 10 percent) covers mixing loss, mortar that skins over before you reach it, and ridges scraped back at flatness corrections.

5. The area with waste is divided by the working coverage and rounded up to whole bags.

A worked example: a 12 ft by 10 ft floor is 120 ft². With a 1/4" x 3/8" square notch for 12 in tile, no back-buttering and 10 percent waste, that is 132 ft² to cover at 63 ft² per 50 lb bag — 2.10 bags, so you buy 3 bags. That is 105 lb of dry mortar and about 16.5 quarts of mixing water.

WHAT YOU CAN DO
- Enter the length and width and read the bags to buy instantly
- Choose from five trowel notches, each with its tile-size guidance and rated coverage
- Turn back-buttering on and watch the coverage and bag count adjust
- Set your own bag weight if you are not buying 50 lb bags
- Choose a waste allowance from 0 to 30 percent with a slider
- See the working coverage, the spread rate in lb per ft², the dry mortar weight in pounds and kilograms, and the mixing water
- Open Details for a full step-by-step breakdown and a coverage table for every notch at your settings
- Learn when a job needs an LFT or medium-bed mortar, and when thin-set beats mastic

BUILT FOR CLARITY
A calm, jobsite-green design puts the bag count first, with the supporting figures right beside it. Area is shown in square feet with the square metre equivalent. Light and dark themes, a tiny download, no clutter and no account required.

AN ESTIMATE, NOT A MATERIALS TAKE-OFF
Coverage figures are typical mid-range values for a polymer-modified thin-set on a substrate flat within 1/4 in in 10 ft. Real coverage changes with the mortar brand, the tile's back profile, substrate flatness, lippage correction and the installer's technique, so always read the data sheet printed on the bag you actually buy. Standards call for at least 80 percent mortar contact on the tile back in dry areas and 95 percent in showers, wet areas and exteriors — pull a tile early and check. This app is for general information and education only and is not professional tiling advice.

PRIVACY
The app collects no personal data and works fully offline. Ads are served by Google AdMob, which may use an advertising identifier as described in Google's policies.

Download Thinset Calculator and know exactly how many bags to throw in the truck.