How much siding do I need?
Siding is priced and ordered by the square — 100 sq ft of wall. The calculator works out the wall area the way an estimator does:
- Walls — perimeter × wall height × number of stories.
- Gables — each gable end is a triangle: half its width × the rise, where the rise comes from your roof pitch. A 28 ft wide gable at 6/12 rises 7 ft and adds 98 sq ft.
- Openings — subtract about 21 sq ft per door, 15 per window and 112 per single garage door.
- Waste — add 10% for cuts, laps and pieces lost at corners; 15% for houses with many angles and dormers.
| House | Walls | Gables | Squares (+10%) | Cartons |
|---|---|---|---|---|
| 40 × 28 ft, 1 story, 2 gables, 10 windows | 1,224 sq ft | 196 sq ft | 13.6 | 7 |
| 50 × 30 ft, 1 story, 2 gables, 12 windows | 1,440 sq ft | 225 sq ft | 15.9 | 8 |
| 30 × 25 ft, 2 stories, 2 gables, 16 windows | 1,980 sq ft | 156 sq ft | 20.4 | 11 |
| 40 × 30 ft, 1 story, hip roof, garage door | 1,260 sq ft | — | 10.6 | 6 |
All with 9 ft walls per story, 6/12 gables and two entry doors.
Vinyl siding calculator: cartons and trim
Most horizontal vinyl siding — double 4 in and double 5 in profiles — comes 2 squares to a carton: for example, 24 panels of 12 ft 6 in double-4 cover 200 sq ft. The calculator rounds your squares up to whole cartons.
Trim is what DIY estimates forget. The calculator adds:
- Starter strip along the bottom of every wall, in 12 ft 6 in pieces.
- Outside corner posts, 10 ft each, stacked on two-story corners.
- J-channel around windows and doors and up the gable rakes.
Count separately: undersill trim below windows, utility trim at the soffit, inside corners, and soffit and fascia if you're replacing them. Ask your supplier for matching accessories in the same color run as the siding.
How to measure a house for siding
Measure each wall at the foundation line with a long tape, and measure the height from the bottom of the existing siding to the soffit — not to the roof. On gables, measure the width at the base and use the roof pitch for the height instead of climbing a ladder; the roof pitch calculator helps if you don't know it.
Our recommendation: don't subtract every small opening on a quote you're comparing. Contractors treat small windows differently, and some don't deduct them at all because the cut-outs are waste anyway. Compare quotes in squares, and ask what's included. Deciding on material first? See vinyl siding vs Hardie board. Re-roofing at the same time? The roofing calculator uses the same footprint, and the gutter calculator finishes the eaves.
