How much grout do you need?
Enter your tile size, joint width, and area to get pounds of grout and the number of bags to buy — instantly, with no sign-up. Also calculates thinset mortar and backer board.
Tile & Area
Grout Joint
Grout Type & Bag Size
How the grout formula works
Step 1 — joint length per unit area (TCNA/Laticrete geometry)
joint_len_per_area = (tile_L + tile_W) / (tile_L × tile_W) [1/in] Each tile shares half its perimeter with its neighbours, netting (L+W) of joint per tile face area L×W. A 12×12 yields 24/144 = 0.167/in; a 2×2 mosaic yields 4/4 = 1.0/in — 6× more grout for the same area.
Step 2 — grout weight per square foot
lb/sq ft = joint_len_per_area × joint_width × joint_depth × density (lb/in³) × 144 Density: sanded 104 lb/ft³ (= 0.0602 lb/in³), unsanded 90 (= 0.0521), epoxy 110 (= 0.0637). Multiplying by 144 in²/ft² converts the per-in² result to per-ft².
Step 3 — total pounds and bags
grout_lb = lb/sq ft × area × (1 + waste%/100) bags = ⌈ grout_lb / bag_size − 1e−9 ⌉ The −1e−9 float guard prevents a spurious extra bag when the result lands on exactly a whole number due to floating-point rounding.
Also need thinset or backer board?
Use the quick links below for your full tile job estimate:
- Thinset Mortar Calculator — 50 lb bags by trowel notch size
- Cement Backer Board Calculator — sheets, screws, tape and bedding
- Grout Sealer Calculator — quarts of penetrating sealer
The tools to grout tile
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Goldblatt 1/4" Square-Notch Tile Trowel
The notch size sets how much mortar lands under the tile — a 1/4" square notch is the common bed the thinset calculator assumes.
Marshalltown 9×4 Gum-Rubber Grout Float (USA)
A gum-rubber float packs grout into the joints and wipes the excess without scratching the tile — sized for the grout amount you just calculated.
Cosmos 1/8" Tile Spacers (500-pack)
Consistent 1/8" joints are what make the grout coverage predictable — the same joint width the calculator used to size your grout.
Miracle 511 Impregnator Grout Sealer (Pint)
Cement grout is porous and stains; a penetrating sealer after it cures keeps the joints clean. A pint covers a typical floor of grout lines.
Marshalltown SC68 Carbide Backerboard Cutter
Cement backer board is scored and snapped, not sawn (which throws silica dust). A carbide scoring tool is the clean way to cut it to size.
QEP Mixing Paddle + 6" Margin Trowel
The paddle mixes thinset and grout to a lump-free consistency on a drill; the margin trowel handles the tight spots a notched trowel cannot.
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Frequently Asked Questions
It depends on your tile size and joint width. For 12×12 tile with a 1/4 in joint at 5/16 in depth (sanded grout at 104 lb/ft³), you need roughly 0.113 lb per sq ft — about 11.3 lb raw, or 12.4 lb with 10% waste. That fits easily in a single 25 lb bag. Mosaic tile (2×2) with the same joint uses exactly 6× more grout per sq ft because of the much higher joint-to-tile-area ratio.
Sanded grout contains silica sand for strength and is used in joints 1/8 in (3 mm) and wider. Unsanded grout is smoother and used in joints narrower than 1/8 in — it will scratch polished surfaces like marble or glass if applied with sanded grout. The densities differ: sanded grout is about 104 lb/ft³, unsanded about 90 lb/ft³, which is why the same joint geometry needs different amounts by weight.
Grout consumption is driven by the ratio of joint length to tile face area. A 2×2 mosaic has 4 in of perimeter per 4 sq in of face — a joint-length-per-area ratio of 1.0 per inch. A 12×12 tile has 24 in of perimeter per 144 sq in of face — a ratio of 0.167 per inch. The mosaic requires exactly 6× more grout per square foot than the large tile at the same joint geometry.
The TCNA/Laticrete formula: grout lb/sq ft = [(tile_L + tile_W) / (tile_L × tile_W)] × joint_width × joint_depth × density (lb/in³) × 144. The 144 converts the per-in² result to per-ft². This is the same formula this calculator uses, with densities of 104 lb/ft³ (sanded), 90 (unsanded), and 110 (epoxy).
Industry standard is 10% for a straight-lay pattern (the Laticrete recommendation). Add 15–20% for diagonal, herringbone, or complex patterns with more cuts. The calculator defaults to 10%; you can adjust up to 30%. Always buy at least one extra bag of the same lot number — grout colour varies between dye lots.
A rubber grout float is the right tool for most joints: it forces grout into the joints, smears the surface evenly, and lets you tool the joints to a consistent depth. Sponges are for cleanup. Very narrow unsanded joints in glass or mosaic sometimes use a squeegee instead. This calculator tells you how many pounds to buy; make sure you have the float to apply it.