Grout is the mortar that fills the gaps between tiles, locks them in place, and keeps water and dirt out of the joint. Yet it is almost always bought by the bag, and estimating how many bags a tile job actually needs is where most DIYers and contractors either come up short or overbuy by 30%. This grout calculator removes the guesswork: enter the square footage of tile, the coverage listed on the bag, the bag size, and the price, and it returns the pounds of grout you need, the whole bags you must buy, and the total material cost.
The math is simple, but the details matter. A bag of sanded grout rated at 5 square feet per pound will cover less if your joints are wider than 1/8 inch, if you are tiling a curved wall, or if you spill half a bucket on the floor. That is why every pro adds a waste allowance — usually 10% — and buys whole bags, never partial ones.
How to Use
- Measure the Total Tile Area in square feet. Multiply length by width for a single rectangle, then add up every wall, floor, or backsplash you are tiling. Do not subtract for outlets or windows on small areas; they barely move the number.
- Find the Grout Coverage printed on the bag you plan to buy. Most sanded grout covers about 3–5 square feet per pound; unsanded grout for narrow joints (under 1/8 inch) covers more, often 6–8 square feet per pound. If you do not know, 5 sq ft/lb is a safe default.
- Set the Waste Allowance. 10% is the industry standard for straight walls. Bump it to 15–20% for large-format tile, diagonal layouts, or intricate mosaics where cuts and scrap are higher.
- Enter the Bag Size in pounds. Bags are commonly sold in 10 lb, 25 lb, and 50 lb sizes. The calculator always rounds up to whole bags, because you cannot buy a fraction of a bag at the store.
- Add the Price per Bag if you want a cost estimate. Leave it at 0 if you only need the quantity.
The result card shows the total pounds of grout required, the number of whole bags to purchase, the total grout cost, and the effective cost per square foot of tile. Use the bags figure at the store, and keep the receipt — unopened bags are returnable at most tile retailers.
The Grout Formula
The estimating method used by tile manufacturers, the Tile Council of North America, and every major bagged-grout brand is straightforward:
Pounds of grout = Tile area (sq ft) ÷ Coverage per pound × (1 + waste%)
Then:
Bags needed = ⌈ Pounds of grout ÷ Bag size (lb) ⌉
where the brackets mean "round up to the next whole bag." Worked example on a 100 sq ft floor with 5 sq ft/lb coverage, 20 lb bags, and no waste: 100 ÷ 5 = 20 lb of grout, and 20 ÷ 20 = 1.0, so you buy 1 bag and spend $15 at $15 per bag. Add a standard 10% waste allowance and you now need 22 lb, which rounds up to 2 bags and $30 — the difference between running out mid-job and finishing on Saturday afternoon.
Coverage figures on bags assume a standard joint width. If your joints are 3/8 inch or wider, you will use roughly twice as much grout as the label suggests; switch to a heavier coverage figure (e.g. 2.5 sq ft/lb) or buy extra.
Examples
Example 1 — A standard bathroom floor. You are tiling a 10 ft × 10 ft bathroom (100 sq ft) with 12 × 12 ceramic tile, 1/4 inch joints, and a 25 lb bag of sanded grout that covers 5 sq ft/lb at $18 per bag. With 10% waste: 100 ÷ 5 × 1.10 = 22 lb; 22 ÷ 25 rounds up to 1 bag; total grout cost is $18. Buying one extra bag is smart insurance, but the calculator says one bag is mathematically enough.
Example 2 — A kitchen backsplash with waste. A kitchen backsplash runs 16 ft wide and 18 inches tall — that is 16 × 1.5 = 24 sq ft. Using unsanded grout at 7 sq ft/lb in 10 lb bags at $12 per bag, with 15% waste: 24 ÷ 7 × 1.15 ≈ 3.94 lb; 3.94 ÷ 10 rounds up to 1 bag; cost $12. Even though you only need 4 pounds, you still buy the whole 10 lb bag — leftover grout is normal for small jobs.
Example 3 — A large commercial floor. A retail space measures 100 ft × 100 ft = 10,000 sq ft, tiled with large-format porcelain at 3/8 inch joints, so you use a conservative 3 sq ft/lb coverage, 50 lb bags at $22 each, and 15% waste. The math: 10,000 ÷ 3 × 1.15 ≈ 3,833 lb; ÷ 50 = 76.67, rounded up to 77 bags; total grout cost is $1,694. At that scale, a second 5% overage buys you a full day of insurance against breakage and color mismatch between pallets.
FAQ
How much grout do I need for 100 square feet?
It depends on the coverage of the product you buy. At the typical sanded-grout coverage of 5 square feet per pound, 100 sq ft requires 20 pounds of grout. With a standard 10% waste allowance, that is 22 pounds — usually 1 to 2 bags depending on whether your bag is 20 lb or 25 lb. At $15 per 20 lb bag, expect to spend about $15–$30.
What is the standard waste percentage for grout?
Most tile professionals use 10% waste as the baseline for straight walls and floors with standard joints. Bump it to 15% for diagonal patterns, large-format tile, or walls with lots of cuts, and to 20% for intricate mosaics or curbless showers where every scrap matters.
Sanded vs unsanded grout — which uses more?
Sanded grout is used for joints 1/8 inch and wider, and because those joints hold more material, it covers less per pound — typically 3–5 sq ft/lb. Unsanded grout is for narrow joints under 1/8 inch and covers more, often 6–8 sq ft/lb. Epoxy grout covers similarly to sanded grout but costs 3–5 times more per bag.
How many square feet does a 25 lb bag of grout cover?
A 25 lb bag of standard sanded grout, at 5 sq ft/lb, covers about 125 square feet of tile in 1/8–1/4 inch joints. At 3 sq ft/lb for wider joints, the same bag covers about 75 square feet. Always check the coverage chart on the specific bag you buy, because formulas vary by brand and joint width.
Should I buy extra bags for a large job?
Yes. On any job over 500 sq ft, buy at least 5% more bags than the calculator returns. Bagged grout can vary slightly in shade between production runs, and having a few identical bags on hand prevents an embarrassing mismatch halfway through. Unopened bags are returnable at most tile and home centers.
Does grout go bad?
Yes. Bagged cement-based grout has a shelf life of about 12 months when stored sealed in a dry location. Once the bag is opened, use it within a few weeks. If the bag feels like a solid brick or shows lumps that do not break apart, the grout has already hydrated and should be discarded — do not try to use it.
Disclaimer
This grout calculator is provided for informational purposes only and does not constitute construction, engineering, or product advice. Coverage figures are estimates based on typical bag labels and standard joint widths; actual coverage varies by tile size, joint width, substrate, and installer technique. Always defer to the coverage chart printed on the bag of grout you actually purchase, and confirm quantities with your tile supplier or a licensed contractor before ordering for a large project.