Add your walls to find out how many squares and boxes of siding you need — for vinyl, fiber cement, and more — with a waste factor and total cost.
Siding covers your exterior walls, so the job is to add up your total wall area and convert it into the units siding is sold in. The method is: measure each wall, add a waste allowance, then divide by 100 to get squares (the standard siding unit). If you know the coverage per box, this calculator also works out the boxes and total cost.
1. Wall area = height × width, for each wall (add gable triangles as ½ × base × height).
2. Total area = sum of all walls.
3. With waste = total × (1 + waste % ÷ 100).
4. Squares = area ÷ 100. Boxes = area ÷ box coverage.
| Siding type | Sold as | Notes |
|---|---|---|
| Vinyl | Box ≈ 2 squares | ~200 sq ft per box |
| Fiber cement | By the plank/square | e.g. Hardie board |
| Engineered wood | By the plank/square | e.g. LP SmartSide |
| Aluminum / steel | By the square | Metal siding |
The squares above cover the flat wall field only. You'll also need J-channel, corner posts, starter strip, and soffit/fascia, which are sold separately by the linear foot. For a home with many windows, doors, and gables, lean toward a 15% waste allowance — every opening and angle creates offcuts you can't reuse.
This calculator uses gross wall area. For large openings like garage doors or picture windows, you can add them as a "negative wall" — just leave one dimension and enter the opening's area mentally, or simply rely on the waste factor to absorb normal-size windows and doors.