How Much Extra Material to Buy

Why waste happens

Every material comes in fixed sizes, and your project almost never divides evenly into them. The last piece in each row is cut to fit, and the offcut may be too short to use elsewhere. Some pieces arrive damaged or warped. Some get cut wrong. Loose materials spill and settle. The waste allowance is a percentage added to the measured quantity to cover these losses.

Typical allowances by project

• Deck boards: 10% for straight rectangular decks, 15% for angles, picture framing or diagonal layouts.
• Fence pickets and rails: 5%, plus enough to build the gates.
• Sod: 5% for rectangles, 8% to 10% for curved beds and obstacles.
• Tile: 10% for straight layouts, 15% for diagonal and large format, 15% to 20% for herringbone.
• Laminate and vinyl plank: 5% to 10%.
• Roofing shingles: 10% for gable roofs, 15% for hip roofs and valleys.
• Drywall: 10% to 15%.
• Concrete: 5% to 10%.
• Pavers: 5% to 10%, more for herringbone and curves.
• Paint: round up to the next gallon. That usually leaves enough for touch-ups.

When to allow more

Raise the allowance for complicated shapes, many corners, diagonal patterns, and materials that break easily, such as natural stone or thin tile. Allow more if you are new to the work, since first projects produce more miscuts. Allow more when materials are delivered and you cannot pick through the pile, and when the product might be discontinued or vary in color between batches, so you will want spares for future repairs.

When to allow less

Large simple areas waste a smaller share of material, because the cuts happen only at the edges. Materials where offcuts can start the next row, like laminate flooring and deck boards on long runs, waste less. And when the store is close and accepts returns, you can buy closer to the measured amount and pick up a little more if needed. Even then, round up to whole units.

Returns and leftovers

Most home centers accept unopened boxes and bags, often within 90 days. Keep receipts, and keep materials dry and in their packaging. Tile, flooring and shingles are worth keeping a box of after the job, labeled with the product name and lot number. Matching an old batch years later is often impossible.

Loose materials like gravel, mulch and soil cannot be returned, but small leftovers are easy to use elsewhere in the yard.

Built into every calculator

Each calculator on this site has a waste or extra field with a sensible default for that material. Change it to match your project's shape and your experience. The Show the math button on each result shows exactly where the allowance was applied.

Calculators for this guide

Results are estimates, not a contractor quote. Check quantities with your supplier before you order, and follow local building codes. Last reviewed 2026-10-12.