Grout Calculator
Updated 2026-10-14
Enter the area you're tiling, the size and thickness of your tiles and the width of the grout joints. The calculator estimates how much grout to buy, including a little extra for waste.
How the grout calculator works
Grout fills the narrow channels between tiles. The amount you need depends on how long those channels are in total, how wide they are, and how deep they are. Deep joints are set by the tile thickness. Small tiles have far more joint length per square foot than large tiles, so they use much more grout.
The calculator works out the volume of the joints, then multiplies by the density of grout to get a weight, because grout is sold by the pound or kilogram. It assumes about 1.8 kg per liter, which is typical for cement-based grout, and adds 10% for mixing and cleanup losses.
Grout weight = joint volume × area × grout density × 1.10
Worked example
A 100 sq ft floor of 12 × 12 inch tiles, 3/8 inch thick, with 1/8 inch joints has about 112.5 cubic inches of joint to fill. At 1.8 kg per liter that weighs about 7.3 lb. Adding 10% for waste gives 8 lb, so one 10 lb or one 25 lb bag is enough.
Quick reference: grout per 100 sq ft
Approximate figures for cement grout, before the 10% waste allowance.
| Tile size | Thickness | Joint | Grout per 100 sq ft |
|---|---|---|---|
| 3 × 6 in (subway) | 5/16 in | 1/16 in | about 9 lb |
| 4¼ × 4¼ in | 1/4 in | 1/16 in | about 7 lb |
| 6 × 6 in | 5/16 in | 1/8 in | about 12 lb |
| 12 × 12 in | 3/8 in | 1/8 in | about 7.3 lb |
| 12 × 12 in | 3/8 in | 1/4 in | about 15 lb |
| 12 × 24 in | 3/8 in | 1/8 in | about 5.5 lb |
| 24 × 24 in | 3/8 in | 1/8 in | about 3.7 lb |
In metric, 30 × 30 cm tiles 8 mm thick with 3 mm joints need about 0.29 kg of grout per m², and 60 × 60 cm tiles 10 mm thick with 3 mm joints need about 0.18 kg per m².
Check your product's coverage chart
Different grouts have different densities. Epoxy grout, urethane grout and some premixed grouts are noticeably lighter or heavier than cement grout, and most manufacturers publish a coverage table on the bag or their website. Use this calculator to get a ballpark figure, then compare it with the manufacturer's chart for your exact product. If they differ, go with the manufacturer.
Sanded or unsanded?
As a general guide, unsanded grout is used for narrow joints of up to about 1/8 inch (3 mm), and sanded grout for wider joints, where the sand adds strength and stops shrinking and cracking. Soft or polished stone can be scratched by sanded grout, so check the tile maker's advice. Many modern grouts are designed to cover a wide range of joint widths, so read the label.
Tips for grouting
- Mix in small batches. Cement grout starts to stiffen within roughly 20–30 minutes, so mix only what you can use in that time.
- Buy one color batch. Like tiles, grout color can vary between batches. Buy enough for the whole job at once.
- Clean the joints first. Scrape out any thinset that squeezed up between tiles so the grout can fill the full depth.
- Seal if needed. Most cement grouts benefit from a sealer once cured, especially in showers and kitchens.
Frequently asked questions
- How much area does a 25 lb bag of grout cover?
- It depends heavily on tile size and joint width. With 12 × 12 inch tiles, 3/8 inch thick and 1/8 inch joints, about 340 sq ft before waste. With 6 × 6 inch tiles of the same thickness and joint width, closer to 170 sq ft.
- Why do small tiles need so much grout?
- Every tile is surrounded by a joint. A square foot of 6 × 6 inch tiles has twice as much joint length as a square foot of 12 × 12 inch tiles, so it needs about twice as much grout.
- What depth should I enter for wall tiles?
- Enter the tile thickness. Grout should fill the joint to the full depth of the tile, finishing flush with or slightly below the surface.