Grout
How Much Grout Do You Need
Grout quantity is almost never “a bag per hundred feet” in a way you should trust. Tile face size, joint width, and joint depth (usually tile thickness on charts) dominate. The grout calculator on this site prefers manufacturer chart cells over a mystery formula—and tells you when it cannot.
Chart cell first
Coverage charts in MAPEI, LATICRETE, TEC, and ARDEX technical data list pack units of grout for combinations of tile size and joint width. When your inputs match a published cell (and joint depth matches the chart’s assumption—typically full tile thickness), the calculator returns that cell. That is the most defensible shopping number: it is the manufacturer’s own table, not our invention.
Presets in grout-products.json store those chart-derived consumption rates. Pack coverage is per published unit (bag, kit, or gallon as the sheet defines). If the sheet in your hand disagrees, believe the sheet and tell us.
When the formula kicks in
Real jobs miss chart rows. Outside an exact cell, the tool may estimate with a calibrated joint-volume formula—but only inside a reliability zone documented in methodology: minimum face at least 3 inches and joint width at most ⅜ inch. Outside that zone you get an explicit warning, not a silent “add 15%” fudge. Calibration checks against chart cells showed the formula usually skews toward extra material; some MAPEI Keracolor mosaic/wide-joint cases can under-estimate—the UI calls that out.
Why tile size and joint width dominate
Think of grout as the network of joints, not as a paint film over the floor. Halving the tile face roughly doubles joint length for the same area. Doubling joint width roughly doubles volume for the same joint length (depth held equal). That is why a bathroom of 1×1 mosaic and a hallway of 12×24 plank are different grout problems even at the same square footage.
I will not paste a homemade pounds-per-square-foot table here. Those tables go stale the moment they disagree with the chart for the product you bought. Open the calculator, pick the preset that matches the bag on the shelf, and read the working.
Documented gap: SPECTRALOCK
LATICRETE SPECTRALOCK PRO Premium points users at a separate coverage card / Project Estimator rather than a stable expanded table we can cite in materials JSON. Until that source is stable and verifiable, the product stays a documented gap instead of a guessed preset. That omission is intentional.
Workflow with the tile tool
- Finish area and piece count in the tile calculator (guide).
- Note actual tile face size, thickness, and joint width you will tool.
- Open the grout calculator with the matching manufacturer preset.
- If you see a zone warning, fix inputs or consult the product chart—do not ignore it.
Tile waste percent is a separate pad (waste guide); do not confuse it with grout overage. Full source hierarchy: methodology.
Sanded, unsanded, and epoxy are not interchangeable
Coverage charts are product-specific because density and packaging differ. Sanded cementitious grout is the usual floor pick for wider joints; unsanded is meant for narrow joints and soft stone that sand would scratch; epoxy packs by kit or gallon with its own table. Mixing a sanded 25 lb chart with an epoxy kit size is how people buy a unit that never matches the joint. Pick the preset that matches the bag or kit on the shelf, not the color name you remember from a different brand.
Joint depth on manufacturer charts usually equals tile thickness. If thinset fills the bottom of the joint, the effective grout depth is less and you need less product — the calculator lets you lower depth when that is your real detail. Do not invent a depth; measure or follow the install method you are using.
Waste on grout versus waste on tile
The grout tool’s waste field is a labeled convention for cleanup, spit buckets, and whole-pack rounding — not the same lever as tile cut waste. Quarry tile and wide joints often want more grout waste than a tight porcelain floor. Change the field when the job is messy; do not silently double-count tile’s floor waste pad as if it were grout. Grout follows the area you will actually joint-fill after the tile is down.
Color-matched repairs later are a dye-lot problem again. Buying an extra small unit of the same batch can be wise on a feature wall; that is attic stock for grout, not a reason to distrust the chart cell for the install day quantity.
Reading the working on the tool
When a chart cell hits, the working should show that you matched a published combination — that is the path you want. When the formula path runs, read the zone note. If the UI warns that you are outside the calibrated face/joint band, stop and open the manufacturer chart or change tile size inputs that were typed in inches wrong (a 12×24 entered as 12×2.4 is a classic fat-finger). Bad inputs create confident nonsense; the warning exists to break that confidence.