Grout Calculator
A grout calculator divides tiled area by 150 sq ft per 25-lb bag and rounds up: an 80 sq ft floor needs 1 bag, and a 350 sq ft job needs 3.
Grout calculator formula
A grout calculator turns the tiled area into a bag count. The formula is bags = area in square feet ÷ 150, rounded up to a whole bag.
The 150 is the coverage this calculator assumes for one 25-lb bag, based on 12 in tile and 1/8 in joints. Grout comes in whole bags, so 0.53 of a bag means you buy one. There is no waste switch because the rounding already leaves you a spare.
Enter the length and width of the tiled area in feet and the price of one bag. You get the bag count and the cost.
Worked examples
Example 1 is a bathroom floor, 10 ft × 8 ft at $18 per bag.
- Area: 10 × 8 = 80 sq ft
- 80 ÷ 150 = 0.53 bags
- Rounded up: 1 bag
- Cost: 1 × $18 = $18
Example 2 is a kitchen floor and backsplash run, 25 ft × 14 ft of tile at $18 per bag.
- Area: 25 × 14 = 350 sq ft
- 350 ÷ 150 = 2.33 bags
- Rounded up: 3 bags
- Cost: 3 × $18 = $54
Notice the second job only needs 2.33 bags. The extra 0.67 bag is your cushion for a wider joint, a few cracked-out joints you have to redo, or a bucket that did not get mixed well.
Bags by tiled area
| Tiled area | Bags (at 150 sq ft per bag) |
|---|---|
| 50 sq ft | 1 |
| 150 sq ft | 1 |
| 151 sq ft | 2 |
| 300 sq ft | 2 |
| 450 sq ft | 3 |
| 600 sq ft | 4 |
At exactly 150 sq ft you get one bag, and one extra square foot gives you two. If your area is close to a multiple of 150, buy the extra bag. Running out in the middle of a floor leaves a color difference between batches.
What changes the real coverage
The 150 sq ft figure is a middle-of-the-road number. Four things move it.
| Factor | Effect on grout needed |
|---|---|
| Smaller tile | More grout, because there is more joint per sq ft |
| Wider joint | More grout, roughly in proportion to width |
| Thicker or deeper tile | More grout, because the joint is deeper |
| Rough or handmade tile | More grout, since the edges are uneven and joints fill unevenly |
A mosaic backsplash can use a bag for a fraction of the area the calculator assumes. Large porcelain panels with 1/16 in joints can use far less. If your tile is unusual, read the coverage chart on the bag or the manufacturer’s site and divide your area by that number instead.
How to measure
- Measure the tiled surfaces only. Skip the area under cabinets and tubs.
- Add each wall or floor section as length × width and total them. A shower with three walls 5 ft, 3 ft and 3 ft wide and 7 ft high is 77 sq ft of wall.
- Include the floor. A 5 ft × 3 ft shower pan adds 15 sq ft, and small floor tile there is grout-hungry.
- Subtract windows, niches and doors only if they are large. For small openings, leave them in as a cushion.
- Tile on a diagonal still uses the same area figure, but the cut edges add joints. Round up.
Common mistakes
- Using the floor area of the room instead of the tiled area. Furniture alcoves and closets that are not tiled should come out.
- Applying the bag figure to mosaics. Check the label first.
- Mixing the whole bag at once. Grout sets in the bucket, so mix what you can spread in about 30 minutes, or follow the working time printed on your bag.
- Buying two different lots for one room. Color can vary between production runs, so buy all the bags at once and check the lot numbers.
- Skipping sealer or cure time. Cementitious grout usually needs sealing after it cures, and the label says when.
Related calculators
Use the tile calculator to count the tiles and the thinset calculator for the adhesive under them. For a full shower, the tile shower cost calculator estimates installed price.
Frequently asked questions
How much coverage does one bag of grout give?
This calculator assumes one 25-lb bag covers 150 sq ft of 12 in tile with 1/8 in joints. Real coverage runs from under 50 sq ft for mosaics and wide joints to several hundred for large tile with hairline joints. The bag label has a coverage chart, so check it against your tile.
How does joint width change how much grout I need?
Grout volume rises with joint width. A 1/4 in joint holds about twice the grout of a 1/8 in joint on the same tile. If your joints are wider than 1/8 in, expect to need more bags than the result shows, and weigh a partial bag of extra against a second trip to the store.
Does tile size affect grout quantity?
Yes. Small tile has far more joint length per square foot. A 1 in mosaic sheet has about 24 ft of joint per sq ft, a 12 in tile has about 2 ft, and a 24 in tile has about 1 ft. Mosaics and subway tile use much more grout than large-format floor tile.
Sanded or unsanded grout, does it change the bag count?
Not in this calculator. Sanded grout is generally used for joints 1/8 in and wider and unsanded for narrower ones, but both come in 25-lb bags with similar coverage claims. Epoxy grout is sold in small kits with their own coverage, so follow the kit instructions.
Why isn't a waste allowance offered for grout?
Grout is mixed in small batches and the bag is the unit, so the rounding up to a whole bag already gives you spare. For 80 sq ft, the result of 0.53 bags becomes 1 bag, which leaves nearly half a bag over. Add a second bag yourself for wide joints or uneven tile.
Estimates only. Verify quantities with your supplier before purchasing.