Grout Calculator: How Much Grout Does Your Tile Job Need?

Grout is the afterthought of every tile project — until you’re halfway through a floor at 9 pm with an empty bucket. The amount you need depends on five variables that interact in non-obvious ways, which is why guessing goes wrong so often. Our grout calculator above handles the math with a standard industry formula and builds in 10% waste.

The Formula Behind the Calculator

Grout fills the network of joints between tiles. The volume of that network per square foot depends on tile size, joint width, and joint depth (which equals tile thickness):

Grout (lbs) = Area × 144 × ((Tile W + Tile L) ÷ (Tile W × Tile L)) × Joint width × Tile thickness × 0.065 × 1.1

All tile dimensions in inches. The 0.065 factor converts cubic inches of joint space into pounds of mixed grout (typical density), and the 1.1 adds 10% for waste — the film you sponge off, the bit that dries in the bucket, and joints that end up slightly wider than planned.

The intuition: small tiles need far more grout than large ones. A floor of 2-inch mosaic has dozens of times more linear joint than the same floor in 24-inch porcelain. Doubling tile size roughly halves grout consumption; doubling joint width doubles it.

Sanded vs. Unsanded Grout

Pick the type before the quantity — they’re not interchangeable:

Sanded grout is for joints 1/8 inch and wider. The sand gives it structure so wide joints don’t crack as they cure. It’s the standard for floors.

Unsanded grout is for joints under 1/8 inch. It’s smoother, sticks better on vertical surfaces, and won’t scratch delicate polished stone or glass tile. Typical for wall tile and backsplashes.

Epoxy grout works at most widths, resists stains dramatically better, and never needs sealing — but costs 3–5× more, cures fast, and is less forgiving for first-timers. Its coverage per pound is similar, but it’s sold in smaller kits; use the pounds from our calculator and check kit yields.

Choosing a Joint Width

• 1/16″–1/8″: rectified (precision-cut) tile, modern minimal look. Use unsanded grout at 1/16″.
• 3/16″–1/4″: standard for most ceramic floor tile; forgiving of small size variations between tiles.
• 3/8″–1/2″: handmade tile, saltillo, and rustic looks — grout consumption rises fast out here.

One practical warning: the joint width you plan and the joint width you get can differ. Non-rectified tiles vary slightly in size, and installers often widen joints a touch to absorb that variation. If your tile is budget ceramic, calculate at the next joint width up.

Practical Tips

Buy one extra pound-unit. Grout is cheap; a color-matched leftover bag is your repair kit for years of cracked-joint fixes.

Note the color code. Like tile dye lots, grout colors vary by batch. Buy all bags at once, same batch if possible, and record the color name for the future.

Mix in small batches. Mixed grout has a working life of 30–60 minutes. Whatever stiffens in the bucket is waste — part of why the 10% margin exists.

Seal cementitious grout (sanded and unsanded) after it cures, especially on floors and in showers. Epoxy needs no sealing.

Frequently Asked Questions

How much grout for 100 sq ft of 12×12 tile? With 1/8″ joints and 3/8″ thick tile: about 8 lbs — one 10 lb bag covers it with margin.

Does grout coverage change with tile thickness? Yes, directly — joint depth equals tile thickness. Going from 3/8″ ceramic to 1/2″ porcelain increases grout needs by a third at the same joint width.

Can I use leftover grout from another project? Only if unopened and stored dry. An opened bag absorbs humidity and may cure weak or lumpy. When in doubt, spend the few dollars on fresh.

Estimates are for planning purposes. Check the coverage chart on your specific grout bag — formulations vary slightly.