Free grout calculator
Estimate how much tile grout your job needs — pounds, bags, and coverage — from your tile size, joint width, thickness, and area, using the published TCNA grout coverage formula. Compare sanded, unsanded, and epoxy grout side by side, with a waste margin built in and every figure updated live, as you type.
On this page14 sections
| Grout type | Pounds | Bags |
|---|---|---|
| Sanded | 27.8 lb | 2 |
| Unsanded | 24.5 lb | 1 |
| Epoxy | 32.7 lb | 2 |
Density factors: sanded ≈ 0.1875, unsanded ≈ 0.165, epoxy ≈ 0.22 lb/in³ (published grout coverage-chart data). Coverage varies by brand and mix; confirm the figure on your bag.
Grout coverage varies by brand, joint and mix. How accurate is this?
Results are estimates. Consult a professional.
How the grout calculator works
Grout fills the joints between tiles, not the tiles themselves, so the amount you need turns on the joints — how many there are and how big each one is. The calculator uses the standard grout coverage formula: it works out the length of joint packed into each square foot of tile, multiplies that by the joint cross-section (width times depth) and the grout's density, then scales it up to your whole area. The result is the pounds of grout needed, the number of bags, and a waste margin on top.
What the result actually means
Two numbers do the work. The pounds figure is the raw amount of grout the joints will hold. The bag count is what you carry out of the store, found by dividing the pounds — plus waste — by the weight of one bag. The calculator shows both so you can see how close your area sits to the next whole bag, because grout is sold by the bag and you cannot buy a third of one.
What goes into your grout estimate
A grout estimate is built from a few measurements. Get each one right and the bag count is right; miss one and you are either short of grout halfway across the floor or left with bags you cannot return.
Tile size — the joint count
Smaller tiles mean more joints per square foot, and more joints mean more grout. A 2-inch mosaic packs six times the joint length of a 12-inch tile into the same area, so it drinks roughly six times the grout. This is why the calculator asks for tile length and width first: tile size sets the joint ratio, the base of the whole estimate.
Joint width — the single biggest lever
Joint width moves the number more than anything else. Going from a 1/8-inch joint to a 1/4-inch joint on the same tile doubles the grout; 1/8 to 3/8 triples it. The calculator takes the joint width straight from the spacers you plan to use, so set it to the size you will actually install, not the size you hope to.
Joint depth — the tile thickness
Grout fills each joint for the full depth of the tile, so joint depth equals tile thickness. A 3/8-inch porcelain plank holds more grout per joint than a 1/4-inch wall tile. Measure the tile edge or read it off the box, and enter that thickness as the joint depth.
Waste factor — the safety margin
Some grout never reaches the joint. It clings to the bucket and the float, dries out before you spread it, and packs unevenly across an imperfect floor. A 10% overage covers it. The calculator adds 10% by default and lets you dial it between 0 and 20%.
A worked example using the grout calculator
Maria is grouting an 80 ft² bathroom floor in 12 in × 12 in porcelain tile, 3/8 in thick, with a 3/16 in joint and sanded grout. She wants the pounds, the bag count for a 25 lb bag, and a 10% waste margin.
Step 1 — Find the joint ratio
Add the tile sides and divide by their product: (12 + 12) ÷ (12 × 12) = 24 ÷ 144 = 0.1667 per in. That is the joint length packed into each square inch of tile face.
Step 2 — Find pounds per square foot
Multiply the ratio by the joint cross-section and density, then scale to a square foot: 0.1667 × 0.1875 × 0.375 × 0.1875 × 144 = 0.3164 lb/ft².
Step 3 — Scale to the whole floor
Across 80 ft²: 0.3164 × 80 = 25.31 lb of grout before waste.
Step 4 — Add waste and count bags
With 10% added, 25.31 × 1.10 = 27.84 lb. Divided by a 25 lb bag and rounded up, that is 2 bags.
How much grout do I need?
If you want a ballpark before you measure, this table gives the area one 25 lb bag of sanded grout covers at a 1/8-inch joint, by tile size. Smaller tiles cover far less per bag because they hold more joints. These are bare coverages — add 10% for waste before you buy.
| Tile size | Grout per 100 ft² (lb) | Coverage per 25 lb bag (ft²) |
|---|---|---|
| 2 × 2 in mosaic | 105 | 24 |
| 3 × 6 in subway | 53 | 47 |
| 6 × 6 in | 35 | 71 |
| 12 × 12 in | 18 | 142 |
| 18 × 18 in | 12 | 213 |
| 24 × 24 in | 9 | 284 |
All figures assume a 1/8-inch (0.125 in) joint, a 5/16-inch (0.3125 in) tile thickness and sanded grout (0.1875 lb/in³). Wider joints, thicker tile or epoxy grout raise the amount; the calculator above adjusts for all four.
When to use this grout calculator
Reach for it any time a tile job turns on how much grout to buy — which is every time, because grout sells by the bag and a half-empty floor cannot wait for a second store run while the first batch sets.
- Tiling a floor — bathrooms, kitchens, entryways and laundry rooms, where joint width and tile size set the bag count.
- Tiling a wall or backsplash — showers, tub surrounds and kitchen backsplashes, often in small or mosaic tile that needs more grout than the area suggests.
- Mixing tile sizes — a feature strip of mosaic in a large-format floor, where you run the calculator once per tile size and add the results.
- Choosing a grout type — to see how sanded, unsanded and epoxy change the amount and the bag count for the same floor.
Sanded vs. unsanded vs. epoxy grout
The coverage math is the same for every grout, but the type changes the density factor — and which one to use depends on the joint, not the math. The three common options trade workability, stain resistance and price.
| Grout type | Best for | Note |
|---|---|---|
| Sanded | Joints 1/8 in and wider, floors | Sand resists shrinkage in wide joints; density ≈ 0.1875 lb/in³ |
| Unsanded | Joints under 1/8 in, polished or soft tile | Smoother, won't scratch delicate faces; density ≈ 0.165 lb/in³ |
| Epoxy | Wet areas, stain-prone, commercial | Waterproof and stain-resistant but pricier and faster-setting; density ≈ 0.22 lb/in³ |
Density factors follow published grout coverage-chart data; epoxy is the densest, so the same joints take the most grout by weight. Confirm the joint range printed on the bag for your tile.
For a wet shower floor or a kitchen counter, epoxy buys long-term stain resistance at a higher price and a shorter working time. For most dry floors, sanded grout is the standard choice and the calculator's default.
Waste factor: how much extra grout to buy
Buy the exact calculated pounds and you will come up short. Grout clings to the mixing bucket and the float, some dries before you can spread it, and an uneven floor packs more into the low joints than the math assumes. A modest overage covers all of it.
The 10% rule
For most jobs, add 10%. On a flat floor with even joints and a careful mixer you can trim to 5%. On a rough wall, a mosaic sheet or anything with irregular joints, 10% is the floor and some installers go to 15%. The calculator's waste field defaults to 10% and adjusts up to 20%.
Why running short is worse than running over
Leftover grout is a few dollars wasted, but running out mid-float is worse: grout sets fast, dye lots vary between bags, and a second batch from a new bag can dry a visibly different shade. Buying the full amount in one lot keeps the color even across the whole floor.
Grout definitions
How accurate is this grout calculator?
The coverage math is the published industry method. The TCNA grout coverage formula — joint ratio times joint width, depth and density, scaled by area — is the same calculation behind the Custom Building Products and MAPEI coverage charts. If your measurements are right, the pounds figure is right to the decimal.
The bag counts are estimates, on purpose. Real coverage drifts with how thickly the grout is mixed, how full the joints pack, and small differences in density between brands and grout lines, so the true count can move a bag either way. Treat the bag count as a planning figure, confirm the coverage printed on your specific bag, and order to the high side — running short mid-float, with dye lots that vary between bags, costs far more than a leftover bag. Pair this with the tile calculator to size the tile order, or the concrete calculator for the slab beneath it.
Frequently asked questions about the free grout calculator
About this grout calculator
This grout calculator runs entirely in your browser — nothing you enter is sent anywhere or stored. It applies the standard TCNA grout coverage formula used in published Custom Building Products and MAPEI coverage charts, recomputing the pounds, bags, and coverage the moment you change a tile size, joint width, thickness, area, or grout type.
It is one of the free estimators in our construction calculators collection. Browse the full library on the calculators home page to size the tile, mortar, and slab for the same job.