Calculators · Grout Calculator

Tile

Grout Calculator

Enter the tile size, joint width and area to get the pounds and bags of grout, with the formula shown.

Unit for tile and joint sizes

Tile length

Tile width

Tile thickness

Fractions work, like 3/8.

Joint width

The real gap between tiles, like 1/8.

Joint depth

Optional. Empty uses the tile thickness.

Area to grout

Grout type

Bag size (lb)

Optional. Used to count bags.

Extra to add (%)

Optional. For waste. Empty means 0.

How to calculate how much grout you need

Grout fills the narrow channel around every tile. So the amount depends on how much joint there is in one square foot of tile, and joint is mostly a matter of how small the tiles are. Many small tiles mean a lot of joint and a lot of grout.

Step	Formula
1. Pitch of one tile	(length + joint) × (width + joint)
2. Share that is joint	1 − (length × width) ÷ pitch
3. Joint volume per ft²	144 × share of joint × joint depth, in cubic inches
4. Pounds per ft²	volume × weight of grout per cubic inch
5. Total pounds	pounds per ft² × area × (1 + extra ÷ 100)
6. Bags	total pounds ÷ pounds per bag, rounded up

The joint depth is normally the tile thickness. If you leave part of the joint filled with setting material, type the real depth in the joint depth box. You can type sizes in inches, with fractions like 1/8 or 3/16, or in millimeters or centimeters.

Where the weight per cubic inch comes from

Volume is geometry, but turning it into pounds needs the weight of the grout. We took it from the coverage charts that Custom Building Products prints in its grout card, which give the square feet one bag covers for each tile size and joint width. The sanded Polyblend chart is written for 25 pounds and the non-sanded Polyblend chart for 10 pounds. Dividing the weight by the joint volume in every cell gives the pounds per cubic inch of joint, and the middle value is 0.0648 lb/in³ for the sanded chart and 0.0619 lb/in³ for the non-sanded one. Those two figures are our calculation, not numbers printed by the manufacturer. We checked the chart in October 2026.

How close is it? For tiles of 4-1/4 inches or larger with joints up to 1/2 inch, the formula lands within about 4% of Custom’s printed coverage in all 30 cells we compared. Small mosaics of 1 inch and joints of 3/4 inch drift further, up to about 20% for the mosaics, so for those use the printed chart of your own grout. Both figures describe one manufacturer’s grouts, so another brand or a premixed grout can weigh differently. If you know the density, choose “Custom density” and type it in pounds per cubic foot. Our tile calculator also estimates grout, but from the coverage table of another product, Mapei Ultracolor Plus FA, which works out at about 0.0573 lb per cubic inch and measures the joint on the nominal tile size. For a 12 by 12 by 3/8 inch tile with a 1/8 inch joint it gives about 6.4 pounds per 100 square feet, against 7.2 pounds here. Each figure follows its own manufacturer’s chart, so use the one that matches the grout you buy.

Example: a 100 sq ft floor of 12 inch tile

The tiles are 12 by 12 inches and 3/8 inch thick, with a 1/8 inch joint. The floor is 100 square feet and you want 10% extra, using the sanded grout figure of 0.0648 lb/in³.

Step	Operation	Result
Pitch	(12 + 0.125) × (12 + 0.125)	147.016 in²
Share that is joint	1 − 144 ÷ 147.016	0.02051
Joint volume per ft²	144 × 0.02051 × 0.375	1.1077 in³
Grout per ft²	1.1077 × 0.0648	0.07178 lb
For 100 ft²	0.07178 × 100	7.18 lb
With 10% extra	7.178 × 1.10	7.90 lb
One 25 lb bag covers	25 ÷ 0.07178	348 ft²

One 25 pound bag is plenty for this floor. Custom’s printed chart gives 348 square feet per 25 pounds for the same tile and joint, so the two agree. These are the figures the calculator shows when you type the same numbers.

Pounds of grout per 100 square feet

Sanded grout at 0.0648 lb/in³, no extra added. The tiles are 1/4 inch thick for the 4-1/4 inch size and 3/8 inch thick for the others, the same thicknesses used in the manufacturer’s chart.

Tile size (in)	1/16 in joint	1/8 in joint	3/16 in joint	1/4 in joint
4-1/4 × 4-1/4	6.71	13.14	19.30	25.20
12 × 12	3.62	7.18	10.68	14.14
6 × 24	4.51	8.92	13.23	17.46
12 × 24	2.72	5.40	8.05	10.68

Read across a row and the pounds roughly double each time the joint doubles. Read down a column and larger tiles need much less. Custom Building Products makes the same point in its technical bulletin TB89 on grout coverage: a joint planned at 1/8 inch that varies by just 1/32 inch changes the grout needed by 25%, and the best way to find the true coverage is a mock-up with your own tile.

How much extra grout to buy

The calculator adds nothing unless you ask. LATICRETE says to add at least 10% of extra grout for waste and clean-up. Custom Building Products adds in TB89 that epoxy grout is mixed in full units, so the excess mix is lost. Type your percentage in the extra box.

Tips for estimating grout

Measure the real joint. Tiles are never exactly the nominal size, and the joint you get may be wider or narrower than the spacer.
Count every surface. For a shower, add each wall and the floor, and run a different floor tile on its own.
Check the thickness. Thick stone and porcelain pavers need more grout than thin wall tile of the same size.
Match the bag size. Ask your seller for the bag size in pounds and type it in the bag box, so the count matches what you can buy.
Need the tile count too? The tile calculator counts tiles and boxes for the same floor or wall.
Need the area? The square footage calculator adds up rooms and shapes.

Frequently asked questions

How do I calculate how much grout I need?

Work out how much joint there is in one square foot of tile. That is the tile and joint size, the joint width and the joint depth, which is usually the tile thickness. Multiply that volume by the weight of the grout, then by your area. A 12 inch by 12 inch by 3/8 inch tile with a 1/8 inch joint needs about 0.072 pounds per square foot with the sanded grout figure used here, so 100 square feet needs about 7.2 pounds.

How many square feet does a 25 lb bag of grout cover?

It depends on the tile size and the joint width. In the coverage chart of Custom Building Products for its Polyblend sanded grout, 25 pounds cover 348 square feet of 12 by 12 inch tile with a 1/8 inch joint, 177 square feet with a 1/4 inch joint and 192 square feet of 4-1/4 inch tile with a 1/8 inch joint. The chart is for estimating only. We checked it in October 2026.

How much extra grout should I buy?

LATICRETE says to add at least 10% for waste and clean-up. Custom Building Products says in its technical bulletin TB89 that there is always a waste factor to consider. Type the percentage you want in the extra box and the result updates.

Does joint width change how much grout I need?

Yes, and by a lot. Grout needed grows with the joint width, so a joint that is 25% wider needs about 25% more grout. Custom Building Products gives the example of a joint planned at 1/8 inch that varies by just 1/32 inch, which changes the grout needed by 25%. Measure the real joint, not just the spacer size.

How do I work out grout for a shower?

Add up the area of each tiled surface, which means every wall plus the floor, then enter the total in the area box. If the floor uses a different tile, run it separately and add the two results. For the areas, use the square footage calculator.

Is concrete grout calculated the same way?

No. This calculator is for tile grout in the joints between tiles. Grout that fills the cores of concrete blocks is measured by volume, and the concrete block calculator handles it.