Material Waste Calculator

Material Waste formula

Waste amount = Measured quantity x waste %
Quantity to buy = Measured quantity x (1 + waste %)
Packages = Quantity to buy / units per package, rounded up
Waste %: 5 brick and block; 10 flooring, tile, drywall, paint, roofing, concrete, lumber, siding; 15 diagonal layouts, large format tile, hips and valleys

Worked example

A 480 sq ft floor in large format porcelain tile: the recommended waste is 15%, so waste is 480 x 0.15 = 72 sq ft and the quantity to buy is 480 x 1.15 = 552 sq ft. If each box covers 12 sq ft, that is 552 / 12 = 46 boxes.

A 2,400 sq ft hip roof with two valleys: at 15% waste, 2,400 x 1.15 = 2,760 sq ft. Shingles are sold by the 100 sq ft square, so 2,760 / 100 = 27.6, and you order 28 squares, or 84 bundles at 3 bundles per square.

Quick reference

Why every job needs a waste factor

A measured area tells you how much material ends up on the floor, wall or roof. It does not count the pieces that never make it there: the cut-off at the end of every row, the tile that cracks when scored, the sheet of drywall that loses a corner in the truck. Those losses are predictable, which is why each trade has a standard allowance. Buying it up front is cheaper than a second trip, and far cheaper than finding the product discontinued or the new box a shade off.

The allowance also covers spares. Flooring, tile and shingles vary between production runs, so a box or two left from the original dye lot is the only way to make an invisible repair later. Store the spares flat and dry and label them with the lot number.

When to go higher than the standard

Push the factor to 15 or 20 percent when the layout has many cuts: small rooms, lots of closets and jogs, diagonal or herringbone patterns, or tile that must be centered on a room. Large format tile and natural stone waste more per cut and break more in handling. Complex roofs with hips, valleys and dormers cut every shingle along the angle. Long plank flooring in a narrow room wastes a full plank width on the last row.

Go lower, around 5 percent, only for simple rectangles with few obstacles, small modular units such as brick and block, or bulk materials such as gravel where the supplier rounds up anyway. When two conditions apply, for instance large format tile laid diagonally, use the higher figure and add a few percent more.

Key facts

• Flooring manufacturers recommend 5 to 10 percent extra for a straight lay and 15 percent or more for diagonal and herringbone patterns.
• Tile setters add 10 percent for standard layouts and 15 to 20 percent for large format, natural stone or diagonal installs where each cut wastes more.
• Tile and flooring vary slightly in color between production runs, so buy the whole job from one dye lot and keep a box for repairs.
• Roofers figure 10 percent waste on a simple gable and 15 percent on roofs with hips, valleys and dormers.
• Brick and block waste is only about 5 percent because units are small, cuts are few, and half units get used at corners.

Frequently asked questions

Sources and references

• •Tile and Natural Stone FAQs, how much extra tile to buy (Daltile)
• •Hardwood Flooring FAQs, how much flooring to order (Bruce)
• •Roof Replacement Costs Explained, waste factor (Owens Corning)