Calculators · Thinset Calculator

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Thinset Calculator

Enter your tile area, pick a mortar and a trowel, and get the bags of thinset to buy from the maker coverage chart.

Length

Width

Thinset product

Sets the bag size and the coverage the maker publishes.

Trowel notch

Only the trowels the maker lists for this product.

Extra to add (%)

Optional. For back-buttering and waste. Empty means 0.

How to calculate how much thinset you need

Thinset, also called thin-set mortar or tile adhesive, is sold in bags that the maker rates by the area they cover. That area is not fixed. It depends on the notch of the trowel, because a deeper notch leaves a thicker bed of mortar and spreads less area. So the calculation is the area of the tile divided by the coverage that the maker gives for your trowel.

Step	Formula
1. Area	length (ft) × width (ft), or the area you already have
2. Area with extra	area × (1 + extra ÷ 100)
3. Bags	area with extra ÷ square feet per bag, rounded up

Makers give the coverage as a range, such as 60 to 67 square feet. The calculator divides by both ends. It shows the number of bags with the low end as the main figure, because that is the one that does not leave you short, and the number with the high end below it.

Example: 200 square feet with a 1/4 by 3/8 inch trowel

A floor is 20 ft by 10 ft and you set it with CUSTOM VersaBond and a 1/4 by 3/8 inch square-notch trowel. The calculator opens with these figures.

Step	Operation	Result
Area	20 × 10	200 sq ft
Coverage, CUSTOM chart	60 to 67 sq ft per 50 lb bag	60 to 67
Bags at the low end	200 ÷ 60 = 3.33, rounded up	4 bags
Bags at the high end	200 ÷ 67 = 2.99, rounded up	3 bags
Weight of 4 bags	4 × 50	200 lb

So the job needs 3 or 4 bags, and 4 is the safe number. With a deeper trowel the same floor takes more. The U-notch trowel held at 30 degrees covers 42 to 47 square feet per bag of the same mortar, so 200 ÷ 42 = 4.76 and 200 ÷ 47 = 4.26 round up to 5 bags either way, or 250 lb.

How many square feet does a bag of thinset cover?

The table lists the coverage that each maker publishes, in square feet per bag, for the trowels it lists. The figures come from CUSTOM Building Products, LATICRETE 254 Platinum (and the 25 lb Platinum Plus) and TEC (Fast Setting, Porcelain and Full Set Plus). The two Skill Set sheets are 2015 copies hosted by Lowe's. All were checked in October 2026. We found no Mapei figures we could open, so Mapei is not in the list. If your mortar is not here, choose “My own coverage” and type the figure from your bag.

Product and bag	1/4 × 1/4 square	1/4 × 3/8 square	1/2 × 1/2 square	3/4 × 9/16 × 3/8 U at 45°	U at 30°	3/16 × 5/32 V
CUSTOM VersaBond Professional, HP or LFT (50 lb)	90 to 100	60 to 67	42 to 47	34 to 38	42 to 47	–
CUSTOM FlexBond, MultiSet, CustomBlend or PremiumPlus (50 lb)	85 to 95	60 to 67	–	–	–	–
CUSTOM Prolite or MegaLite (30 lb)	90 to 100	63 to 70	45 to 50	36 to 40	45 to 50	–
LATICRETE 254 Platinum (50 lb)	80 to 95	60 to 70	35 to 40	–	–	–
LATICRETE 254 Platinum Plus (25 lb)	80 to 95	60 to 70	35 to 40	–	–	–
TEC Skill Set Fast Setting (50 lb)	96 to 106	66 to 76	–	–	–	150 to 160
TEC Skill Set Porcelain (50 lb)	80 to 90	55 to 65	–	–	–	130 to 140
TEC Full Set Plus, unmodified (50 lb)	95 to 105	65 to 75	–	–	–	–

Note that the LATICRETE Platinum Plus bag weighs 25 lb and the LATICRETE sheet says it has the coverage of a 50 lb bag of traditional mortar. The bag size is part of the figure, so the calculator shows the weight of the bag with the result.

Which trowel for which tile?

The amount of thinset follows the trowel, and the trowel follows the tile. For large tiles, CUSTOM publishes a rule on the page of its FlexBond LFT mortar (checked October 2026):

Longest side of the tile	Trowel	Sq ft per 50 lb bag
8 to 15 in	1/4 × 3/8 × 1/4 in square-notch	63 to 70
More than 15 in	1/2 × 1/2 × 1/2 in square-notch	45 to 50
More than 15 in	3/4 × 9/16 × 3/8 in U-notch	36 to 40

Those figures are for that one mortar, so they differ a little from the VersaBond ones above. The same chart says “Back buttering may be necessary,” and it asks for mortar coverage under the tile of at least 80% in dry areas and at least 95% in wet areas and exteriors. CUSTOM also does not recommend the 1/2 inch square-notch trowel, because the 1/2 inch gap between notches makes it harder to bed the tile. It suggests a deeper U-notch or V-notch trowel that lets the ridges collapse, and says the 3/4 inch U-notch held at 30 degrees gives the same coverage area as the 1/2 inch trowel.

What this calculator does not count

It does not estimate the extra mortar for back-buttering, because no maker gives a figure. Type your own percentage in the extra box if you plan to do it. It does not size grout, tile or backer board, and it does not show prices, which change by region and store. For the number of tiles and boxes, use the tile calculator. For the grout, use the grout calculator. To work out the area first, use the square footage calculator.

Tips for ordering

Take the coverage from the data sheet of the exact mortar and the exact trowel you plan to use.
Use the low end of the range when the surface is uneven or you want some margin.
Lift a tile now and then and check the mortar on its back, as the LATICRETE and TEC data sheets advise.
Thinset is not the same as mortar for brick and block. For that, see the mortar calculator.

Frequently asked questions

How do I calculate how much thinset I need?

Find the area to tile in square feet, then divide it by the coverage of one bag. The coverage is not one number. It depends on the mortar and on the notch size of the trowel, so take it from the data sheet or the chart of the mortar you buy. For 200 square feet with a 1/4 by 3/8 inch square-notch trowel and CUSTOM VersaBond, which covers 60 to 67 square feet per 50 lb bag, you need 200 ÷ 60 = 3.33 bags at the low end, so 4 bags.

How many square feet will 50 lb of thinset cover?

It depends on the trowel and the product. In the charts we checked in October 2026, a 50 lb bag covers 80 to 106 square feet with a 1/4 by 1/4 inch square-notch trowel, 55 to 76 square feet with a 1/4 by 3/8 inch trowel and 35 to 47 square feet with a 1/2 by 1/2 inch trowel. A deeper notch spreads more mortar, so a bag goes less far.

How much thinset do I need for 12x24 tile?

The tile size does not set the amount directly. It sets the trowel. CUSTOM Building Products says that when the longest side of the tile is more than 15 inches you use a 1/2 inch square-notch or a 3/4 inch U-notch trowel, and that back-buttering may be needed. A 12 by 24 inch tile has a 24 inch long side. For 200 square feet with the U-notch trowel held at 30 degrees, which covers 42 to 47 square feet per 50 lb bag of CUSTOM VersaBond, you need 5 bags either way.

How much thinset should I mix at a time?

We found no manufacturer figure for batch size that we could cite, so the calculator does not give one. Mix only as much as you can spread and set before it skins over. LATICRETE says that if the mortar has skinned over and is not sticky, you remove it and replace it with fresh mortar. Open time is on the data sheet of your product.

Does the tile size change how much thinset I need?

Yes, through the trowel. CUSTOM says tiles with a longest side from 8 to 15 inches take a 1/4 by 3/8 inch square-notch trowel, and tiles with a longest side of more than 15 inches take a 1/2 inch square-notch or a 3/4 inch U-notch trowel. A deeper notch leaves more mortar on the floor, so one bag covers fewer square feet. Pick the trowel in the calculator and the bags change with it.

Do I need extra thinset for back-buttering?

Probably, but no maker gives a figure. CUSTOM states that its coverage chart does not include back-buttering and tells you to consider the pattern and depth of the underside of the tile. Estimate it yourself and type it in the extra box as a percentage. The calculator adds it to the area before dividing.