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Grout Calculator

Pounds (kg) of grout and number of bags for your tile size, thickness and joint width.

How this is calculated

Joint volume per tile = (L + W) × joint width × tile thickness. Volume per ft² = 144 × (L + W) × J × T ÷ (L × W). Weight = volume × grout density × (1 + waste).

Grout use depends on tile size, tile thickness and joint width. Enter those, pick the grout type and bag size, and get the total grout needed, number of bags, joint length and cost.

Results are estimates for planning purposes only. Real-world quantities depend on site conditions, materials and workmanship. Always verify measurements, follow local building codes and confirm quantities with your supplier or a qualified professional before ordering or building.

About the Grout Calculator

Grout looks like a minor purchase until you are floating a 200-square-foot floor and the bucket runs dry. Coverage swings wildly: a bag covering 200 square feet of large tile with tight joints may cover only 40 square feet of mosaic with wide joints. This calculator uses your tile size, joint width and area to estimate grout in pounds and bags, for sanded and unsanded grout alike.

How to use

  1. Enter the total tiled area in square feet — the same area used for the tile calculation.
  2. Enter tile length and width in inches, for example 12 by 12 or 3 by 6 subway tile.
  3. Enter joint width: 1/16 inch for tight modern joints, 1/8 as the standard, 1/4 or more for rustic looks.
  4. Enter the tile thickness (joint depth) — grout fills the joint down to the tile bed.
  5. Choose sanded or unsanded grout; the calculator adjusts coverage since sanded grout is denser.

Understanding your results

Total grout is shown in pounds — the honest unit, since bag sizes vary. The bag count converts that into 10 lb or 25 lb bags, rounded up. The coverage note gives effective square feet per bag for your exact tile and joint combination. Buy all bags from the same batch for consistent color.

How the calculation works

The calculator totals all joint length: each tile contributes half its perimeter in shared joints, times the tile count. Joint volume is that length times joint width times depth, converted to weight using mixed-grout density. A 10 percent waste allowance covers sponge cleanup, and the total divides by bag size and rounds up.

Grout Calculator FAQs

Use sanded grout for joints 1/8 inch and wider — the sand prevents shrinkage and cracking in wide joints and it is the standard for floors. Use unsanded grout for joints under 1/8 inch, common on polished stone and wall tile, where sand would scratch the surface or fall out of tight joints. Never use sanded grout on polished marble or soft stone.
One 10 lb bag is usually plenty. A 30 square foot backsplash with 3×6 subway tile and 1/16-inch joints uses roughly 3 to 5 pounds of grout — the tight joints and small area keep consumption low. Buy the 10 lb bag rather than a 25 lb one: grout has a shelf life of about a year, and an opened bag hardens with humidity.
Roughly 150 to 200 square feet for standard 12×12 tiles with 1/8-inch joints. But switch to 2×2 mosaic with 1/8-inch joints and the same bag may cover only 40 to 60 square feet, because small tiles mean far more joint length per square foot. Joint width matters just as much — doubling the width roughly doubles the grout needed.
Wait 24 to 72 hours before sealing cement grout — check the product label, since times vary. Showers should stay dry for at least 72 hours so the grout cures fully before constant water exposure. Sealing too early traps moisture and causes blotchy color; skipping sealer on cement grout leaves it stain-prone.
The most common causes are too much water in the mix, which weakens grout as it dries, and movement in the substrate — a flexing subfloor or missing expansion joints. Grout should never fill the joint where tile meets a wall, tub or change of plane; those need flexible caulk. Cracking in wide joints often means unsanded grout was used where sanded was required.
Nabil Sharif, founder of CalcDune

Written by

Nabil Sharif

Founder of CalcDune — a free library of 137 online calculators for finance, health and everyday math. Every calculator shows the formula behind its result, so you can see exactly how your numbers are worked out.

More articles by Nabil →

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