How to use the grout calculator
- Enter the area to tile.
- Enter the tile width, length and thickness.
- Enter the joint width you will use.
- Keep about 10% extra for mixing and cleanup.
The result is the volume of grout the joints hold. Compare it with the coverage chart on the grout you buy, which lists coverage for common tile sizes and joints. Mix grout in small batches as you go. The result from Decoratoradvice is the total for the job, not how much to mix at once.
Grout formula
Joint length per unit area = (tile width + tile length) ÷ (tile width × tile length)
Grout volume = area × joint width × tile thickness × joint length per unit area
Smaller tiles and wider joints need more grout, because there is more joint for every square foot.
Worked example
40 sq ft of 12 × 12 in tiles, ⅜ in thick, ⅛ in joints:
Joint length per sq in: (12 + 12) ÷ (12 × 12) = 0.167 in per sq in
Per sq ft: 144 × 0.125 × 0.375 × 0.167 = 1.13 cu in
For 40 sq ft: 45 cu in
With 10% extra: about 50 cu in (0.81 L)
How tile size changes grout
For ⅜ in thick tile with ⅛ in joints, per square foot:
| Tile size | Grout per sq ft |
|---|---|
| 2 × 2 in mosaic | 6.8 cu in |
| 3 × 6 in | 3.4 cu in |
| 6 × 6 in | 2.3 cu in |
| 12 × 12 in | 1.1 cu in |
| 12 × 24 in | 0.8 cu in |
Tips
- Use the same tile size and joint you entered in the tile calculator.
- Sanded grout is generally used for wider joints and unsanded for narrow ones; follow the grout manufacturer's joint-width range.
- Mix small batches; grout stiffens as you work.
- Seal cement grout if the manufacturer recommends it.
Common mistakes
- Using tile area instead of joint volume. Grout fills the joints only.
- Ignoring tile thickness. Thicker tile means deeper joints.
- Confusing grout with mortar. Masonry mortar bonds bricks and blocks; see the mortar calculator.
Frequently asked questions
How much grout do I need for 100 sq ft?
For 12 × 12 in tile, ⅜ in thick with ⅛ in joints: about 113 cu in, or 124 cu in with 10% extra.
Does joint width change the amount of grout?
Directly. Doubling the joint width from ⅛ in to ¼ in roughly doubles the grout.
Why do mosaics need so much grout?
Small tiles have far more joint per square foot. A 2 × 2 in mosaic needs about six times as much grout as 12 × 12 in tile.
How do I convert the volume to bags?
Check the grout bag's coverage chart for your tile size and joint, or its yield if stated, and divide.
Can I use this for a backsplash?
Yes. Enter the backsplash area and the tile's dimensions. The flooring calculator and tile calculator cover the floor.
Key takeaways
- Grout volume depends on joint width, tile thickness and tile size.
- Smaller tiles need much more grout per square foot.
- Add about 10% extra.
- Check the result against the coverage chart on your grout.