Measuring the exterior
The roof and walls are both measured in squares — 100 square feet each — so a roof or siding job comes down to total area plus a waste allowance, with roofing adjusted for pitch (a steeper roof has more surface than its footprint). Gutters follow the length of your eaves, with downspouts spaced to drain the roof. Roof work is dangerous, so for steep or complex roofs, get a professional measurement.
Which calculator do I need?
- Roofing calculator — squares and bundles of shingles from your roof footprint and pitch.
- Roof pitch calculator — pitch, angle, slope factor, and rafter length from rise and run.
- Siding calculator — squares and boxes of siding for the walls, minus openings.
- Gutter calculator — gutter sections, downspouts, and hangers for your eaves.
It's more than the visible material
An exterior estimate has to include the parts you don't see. A roof needs underlayment, drip edge, starter and ridge shingles, and flashing beyond the field bundles; siding needs house wrap, J-channel, corner posts, and starter strip; and gutters need downspouts, elbows, and end caps. Add a waste allowance too — 10% for simple shapes, 15%+ for roofs and walls with lots of hips, valleys, gables, and corners. Because roof work is dangerous, measure from the ground or attic where you can, and hire a pro for steep or complex roofs.