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Siding is ordered by the square — 100 square feet of wall. The Siding Calculator multiplies the perimeter of the house by the wall height, adds each gable triangle (width² × pitch ÷ 48), subtracts a typical 15 sq ft per window and 20 sq ft per door, and adds a waste allowance, usually 10%. Vinyl siding comes in cartons: a carton of double 4 in panels — 24 panels 12 ft 6 in long with an 8 in exposure — covers 200 sq ft, or 2 squares. Fiber cement lap siding such as HardiePlank comes in 12 ft planks, each covering 12 ft times its exposure; with the 1 1/4 in minimum lap of IRC R703.10.2 the 8.25 in plank shows 7 in and covers 7 sq ft, so a square takes 14.3 pieces. A 40 × 30 ft house with 9 ft walls, two 6/12 gables, 10 windows and 2 doors has 1,295 sq ft of wall — 14.25 squares with waste, 8 cartons of vinyl or 204 HardiePlank 8.25 in planks, plus 140 ft of starter strip, 36 ft of outside corners and 194 ft of J-channel.
Siding is ordered by the square (100 sq ft). Wall area = perimeter × wall height + gable triangles (width² × rise ÷ 48 each) − openings (typical window 15 sq ft, door 20 sq ft), plus about 10% waste. A carton of double 4 in vinyl siding (24 panels × 12 ft 6 in, 8 in exposure) covers 200 sq ft. Fiber cement lap planks are 12 ft long and cover 12 ft × exposure; exposure = plank width − the 1 1/4 in minimum lap of IRC R703.10.2.
| Plank width | Exposure | Coverage per plank | Pieces per square |
|---|---|---|---|
| 12 in | 10.75 in | 10.75 sq ft | 9.3 |
| 5.25 in | 4 in | 4.00 sq ft | 25.0 |
| 6.25 in | 5 in | 5.00 sq ft | 20.0 |
| 7.25 in | 6 in | 6.00 sq ft | 16.7 |
| 8.25 in | 7 in | 7.00 sq ft | 14.3 |
| 9.25 in | 8 in | 8.00 sq ft | 12.5 |
Multiply the perimeter by the wall height, add the gable triangles (width² × rise ÷ 48 each), subtract windows and doors, then add about 10% for waste. Divide by 100 for squares. A 40 × 30 ft house with 9 ft walls, two 6/12 gables, 10 windows and 2 doors has 1,295 sq ft of wall — 14.25 squares with waste.
A carton of double 4 in vinyl siding usually holds 24 panels 12 ft 6 in long with an 8 in exposure — 200 sq ft, or 2 squares (CertainTeed MainStreet and Monogram spec sheets). Divide your square footage with waste by 200 and round up: 1,424.5 sq ft needs 8 cartons. Check the label, since some profiles pack fewer squares.
Each 12 ft HardiePlank covers 12 ft × its exposure. The 8.25 in plank laps 1 1/4 in and shows 7 in, so it covers 7 sq ft and a square takes 14.3 pieces. The 6.25 in plank (5 in exposure) takes 20 per square and the 12 in plank (10 3/4 in exposure) 9.3.
At least 1 1/4 in under IRC R703.10.2, with butt joints caulked, covered with a joint cover or backed with flashing. That lap is why an 8.25 in plank gives a 7 in exposure.
100 square feet of wall coverage, the same unit used for roofing. Siding is priced and ordered by the square, so a 1,425 sq ft order is 14.25 squares.
Painting instead? The exterior paint calculator turns the same wall area into gallons.
Prefer a cement finish? The stucco calculator counts base and finish bags, lath and weep screed.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.