The amount of grout depends mostly on tile size and joint width: small mosaics with wide joints use many times more grout per square foot than large-format tiles with ⅛ in joints. The joint depth is normally the tile thickness. Sanded grout is used for joints ⅛ in and wider; unsanded for narrower joints.
How to use the Grout Calculator
- Tiled area
- Tile length
- Tile width
- Joint width
- Joint depth (tile thickness)
- Grout density
- Waste
- Bag size
- Price per bag
- Every result field is editable: type into Grout needed and Joint width plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the tiled area, tile length, width and thickness (joint depth), joint width, grout density, bag size and price. The calculator finds the total length of joints per unit area, multiplies by the joint cross-section and converts to weight and bags.
Tips for an accurate estimate
- Measure the formwork, not the drawing – forms bulge and subgrades are rarely perfectly flat, so add 5–10%.
- Below about 1 cubic yard, premixed bags are usually cheaper; above that, ready-mix saves time and gives a more consistent pour.
- Order ready-mix in quarter- or half-yard steps and ask about short-load fees for small deliveries.
- Keep fresh concrete damp for at least a week – curing matters as much as the mix for final strength.
Common mistakes to avoid
- Running short mid-pour, which leaves a weak cold joint.
- Adding extra water on site to make concrete easier to place – it lowers strength and increases cracking.
- Ignoring the volume of rebar, posts or pipes in the pour, or the gravel base under it.
Inputs explained
| Field | What to enter |
|---|---|
| Tiled area | Units: ft², m², yd², acre |
| Tile length | Units: in, cm, mm, ft, m, mm |
| Tile width | Units: in, cm, mm, ft, m, mm |
| Joint width | Units: in, cm, mm, ft, m, mm |
| Joint depth (tile thickness) | Units: in, cm, mm, ft, m, mm |
| Grout density | Units: kg/m³, lb/ft³, g/cm³, lb/yd³ |
| Waste | In % |
| Bag size | Choose one: 25 lb, 10 lb, 5 kg, 20 kg |
| Price per bag | Units: /piece |
What each result means
- Grout volume = [Tiled area]×([Tile length] + [Tile width])÷([Tile length]×[Tile width])×[Joint width]×[Joint depth (tile thickness)]
- Grout needed = [Grout volume]×[Grout density]×(1 + [Waste]÷100)
- Bags = ceil([Grout needed]÷[Bag size])
- Coverage per bag = [Bag size]÷[Grout needed]×[Tiled area]
- Cost = [Bags]×[Price per bag]
Example values
How the main result changes when Joint width changes and everything else stays at the example values above:
| Joint width (in) | Grout needed (lb) |
|---|---|
| 0.0625 | 4 |
| 0.0938 | 6 |
| 0.125 | 8 |
| 0.1563 | 10.1 |
| 0.1875 | 12.1 |
| 0.25 | 16.1 |
Formula
Grout volume = area × (L + W) ÷ (L × W) × joint width × joint depthWeight = volume × grout density × (1 + waste)Worked example
Inputs — Tiled area: 100 ft²; Tile length: 12 in; Tile width: 12 in; Joint width: 0.125 in; Joint depth (tile thickness): 0.375 in; Grout density: 1,800 kg/m³; Waste: 10 %; Bag size: 25 lb; Price per bag: $25 /piece.
Results — Grout volume = 112.5 in³; Grout needed = 8 lb; Bags = 1; Coverage per bag = 311 ft²; Cost = $25.00.
Frequently asked questions
How much grout do I need for 100 ft² of 12 in tile?
With ⅛ in joints and ⅜ in tile, about 6 lb – one 10 lb bag with room to spare.
Sanded or unsanded grout?
Sanded for joints ⅛ in (3 mm) and wider, unsanded for narrower joints and polished stone that could scratch.
Why does mosaic tile use so much grout?
Small tiles have far more joint length per square foot.
What formula does the Grout Calculator use?
Grout volume = area × (L + W) ÷ (L × W) × joint width × joint depth.