Estimate only. It includes 10% extra for waste. Rough or uneven tiles and wider joints use more grout.
How to use this calculator
Enter the tiled area, the tile size, the tile thickness and the grout joint width. Press Calculate to see the pounds of grout and the number of bags to buy.
The formula
Joint length per sq ft = (tile length + tile width) ÷ (tile length × tile width) × 144
Grout volume = area × joint length × joint width × tile thickness
Grout weight = volume × 0.0579 lb per cubic inch, plus 10% waste
Example: 100 sq ft of 12 in × 12 in tiles, 3/8 in thick, with 1/8 in joints needs about 7.2 lb of grout, so one 10 lb bag is enough.
What affects how much grout you need
This calculator estimates grout by weight. It works out the total length of grout joints, multiplies by the joint width and tile thickness to get the volume, then converts that to pounds and adds 10% for waste. The result tells you how many bags to buy.
Why tile size matters so much
Grout fills the gaps between tiles, so more tile edges mean more grout. Here is a quick comparison. 100 sq ft of 12 in by 12 in tile, 3/8 in thick, with 1/8 in joints needs about 7.2 lb of grout. Now take only 50 sq ft of 3 in by 6 in subway tile, 1/4 in thick, with the same 1/8 in joints. It also needs about 7.2 lb. Half the area, the same grout, because small tiles have three times as many joints per square foot.
Main factors that change the result
- Tile size: Smaller tiles and mosaics need far more grout per square foot.
- Joint width: Doubling the joint from 1/8 in to 1/4 in doubles the grout.
- Tile thickness: Thicker tiles have deeper joints to fill.
- Tile edges: Rough, tumbled or handmade tiles have irregular joints that use more grout.
Tips and common mistakes
- Use the actual tile thickness, not the nominal size on the box.
- Measure the real joint width from your spacers.
- Mix only what you can use within the working time on the bag. Grout that starts to set should not be re-mixed with water.
- Clean excess thinset out of the joints before grouting so the grout can fill to full depth.
- Wipe the haze off the tile with a damp sponge before it hardens.
Choosing and buying grout
Pick the grout type that fits your joints and location. Sanded grout suits wider joints, while unsanded grout suits narrow joints. Epoxy and premixed grouts cost more but resist stains better, which can be worth it on kitchen counters and shower floors. Buy grout from the same batch for the whole job to keep the color consistent. Color can look different when dry, so check the color chart or make a small test sample. A small amount of extra grout is useful for future repairs. Plan to seal cement-based grout if the manufacturer recommends it, especially in wet areas.
