Flooring Calculators

Floor coverings are sold against charts, and a chart only covers the sizes somebody chose to put on it.

The calculators

• Carpet CalculatorCRI 105 sections 5.1 and 5.2, quoted in full
• Tile CalculatorGrout coverage derived from the geometry a manufacturer's chart is made of

Almost every flooring quantity is settled by a manufacturer's chart: so many square feet per bag, so many pieces per box, this much waste for that layout. The charts are usually right. The problem is that they are lists, and a list runs out.

Large format tile, odd rectangles, plank sizes that did not exist ten years ago: none of them are on the chart you are holding, and the trade answer is to pick the nearest row and hope. So the pages here work out what generates the chart, and then use that instead.

It usually turns out to be one number

Grout coverage is the clearest case. Laticrete's chart has 69 cells across 23 tile sizes and three joint widths. Run every cell backwards and they all imply the same bag volume, 141.8 cubic inches, because the chart is that volume divided by the exact geometry of the joint. Compute it forward for a tile the chart does list and you land on the published cell. Compute it for one the chart does not list and you have an answer where before there was a guess.

The error that doubles a grout order

A tile shares each joint with its neighbour, so the footprint it claims is the tile plus one joint in each direction, not two. Counting a full joint on all four sides roughly doubles the grout figure, and it is the likeliest reason the numbers circulating for the same tile and joint disagree by more than half.

Waste is a layout question, not a material one

The usual 10% assumes a square room laid straight, where the offcut from one end of a run starts the next. A diagonal layout cuts every perimeter tile into a triangle that fits nowhere, and a pattern with a repeat needs specific offcuts rather than whatever is left. Neither is covered by the flat allowance, and neither is a property of the tile.

What is not here

Substrate flatness tolerance, which lives in ANSI A108 and is not a free document, and which is the real cause of most large format complaints. Thinset coverage, which is published per trowel notch rather than per tile. And movement joints, which are a design decision and not optional on a large floor.