How to Estimate Bricks, Stairs, and Roofing Materials
The material-estimation formulas behind brick counts, stair rise/run, and roofing squares, worked through with real projects.
Brick counts, stair dimensions, and roofing materials each start from a different physical constraint, but all three end in the same basic pattern: calculate the raw requirement, then round up for real-world waste and practical constraints.
Brick calculator: area times density
Bricks Needed = Wall Area × Bricks per Sq Ft × (1 + Waste%). A 20ft × 8ft wall (160 sq ft) using standard modular brick (about 7 bricks per square foot with mortar joints) and a 10% waste allowance: 160 × 7 × 1.10 = 1,232 bricks.
Stair calculator: rounding to a whole number of steps
Given a total rise of 108 inches and a target step rise of 7.5 inches, the number of steps is round(108/7.5) = round(14.4) = 14 steps. Because the step count must be a whole number, the actual rise per step adjusts slightly: 108/14 ≈ 7.71 inches — very close to, but not exactly, the original 7.5-inch target, since the total rise had to be divided evenly across a whole number of steps.
Roofing calculator: squares, not square feet
Roofing materials are estimated in "squares" — 100 square feet each, a trade-specific unit rather than raw square footage. A 2,000 sq ft roof with a 10% waste allowance needs 2,000 × 1.10 = 2,200 sq ft covered, which is 2,200/100 = 22 squares. At roughly 3 shingle bundles per square, that's 22 × 3 = 66 bundles of shingles.
Why rounding direction matters differently for each
Bricks and roofing bundles should always round up — a partial bundle or brick still requires buying the whole unit. Stair steps round to the nearest whole number (not always up), since the actual rise-per-step then adjusts to fit whatever whole step count results, rather than the step count itself needing a safety margin.
Common mistakes to avoid
- Forgetting that roofing waste percentage should typically be higher for complex roof shapes (multiple valleys, hips) than for a simple gable roof
- Assuming stair rise adjusts to exactly the target value rather than recalculating around the rounded step count
- Ordering bricks or bundles at the exact calculated minimum with zero waste allowance, risking a stalled project if a delivery falls short mid-build
Estimate your own project with the brick calculator, stair calculator, and roofing calculator.