Grout coverage changes with tile size, joint width and tile thickness. This tool gives a rough comparison using a reference coverage of 90 square feet per 25 lb bag for 12-inch tiles with 1/8-inch joints.
Use the coverage chart for your actual grout to make the final order. Very deep joints, mosaics and textured tiles can need a different amount.
How to use this calculator
- Measure the tiled area and note the tile dimensions from the box.
- Measure your joint width with the spacers you actually used — do not guess from memory.
- Calculate, then buy to the rounded-up figure so one batch covers the whole room.
- Mix grout in small batches; a full 25 lb bag can start to set before a beginner finishes spreading it.
How the grout estimate works
Reference coverage is 90 sq ft per 25 lb bag for 12x12 inch tiles with a 1/8-inch joint. Bags = (area ÷ 90) × (joint width ÷ 0.125) × tile-size factor × (1 + allowance ÷ 100). Tile-size factor = ((12 ÷ max(tile length, 1)) + (12 ÷ max(tile width, 1))) ÷ 2, with tile measurements in inches. Dimensions below 1 inch are treated as 1 inch in this comparison. The formula does not use tile thickness, joint depth or product density; use the actual grout coverage chart for the final order.
A 100 sq ft floor of 12x12 tiles with 1/8 inch joints sits right on the reference point: about 1.11 bags before allowance, and 1.22 bags with 10 percent added — so buy 2 bags and keep the second as your reserve if the first stretches further than expected.
A few things worth checking
- Assuming the grout left over from a large-tile job will stretch to a mosaic — small tiles can use three times as much grout per square foot.
- Mixing two different grout brands or batches on one visible floor; colour can differ enough to show.
- Skipping the allowance for what stays on the sponge and the sides of the bucket — sponging loss is real, typically a tenth or more of what you mix.
Your questions, answered
What bag size does the estimate use?
It uses a 25 lb reference bag, with 90 sq ft coverage for 12x12 inch tiles and a 1/8-inch joint. The reference is an estimate built into this tool, not a coverage promise for every grout product.
Does it account for tile thickness or joint depth?
No. The inputs are area, tile face dimensions, joint width and an extra allowance. Tile thickness, joint depth and product density are not entered, so this tool cannot reproduce every manufacturer coverage chart.
Why does my estimate differ from the chart on the bag?
The tool scales a fixed reference using joint width and a tile-size factor. It also treats tile dimensions below 1 inch as 1 inch in that factor, so it is not a precise model for very small mosaics. Use the chart for your actual tile, joint and grout as the final quantity check.
How much water do I mix with grout?
No mixing-water quantity is calculated here. Follow the current mixing instructions for your exact grout product. The bag estimate does not select a grout type or an installation method.
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