Loan Siding Estimator
Siding is ordered in squares, boxes, planks and lineal feet — never in "walls". Measure the perimeter, subtract the openings, pick your material, and get the buy quantities with waste figured in.
Openings are subtracted at standard sizes — 15 sq ft per window, 21 sq ft per door. Gables: add the triangle area (half of width × peak height) by raising the wall height on gable walls, or run those walls separately.
The same walls, in every material
| Material | You buy |
|---|---|
| Run the numbers to compare buy quantities. | |
Trim, J-channel, starter strip and corner posts are lineal-foot items measured off the building itself — your supplier works them out from the same perimeter and opening counts.
How it works
Start with gross wall area (perimeter × height), subtract openings at 15 sq ft per window and 21 sq ft per door, then add the waste allowance. Vinyl is priced in squares (100 sq ft) and boxed at 2 squares per box. Fiber-cement plank at a 7-in exposure covers 7 sq ft per 12-ft board (12 × 7⁄12). Wood lap at 6½-in exposure needs 12 ÷ 6.5 ≈ 1.85 lineal feet of board per sq ft. Exposure is the visible part of each course — the rest hides under the course above, which is why "board size" and "coverage" are never the same number in siding.
Formula & worked example
Formula: Net area = (perimeter × height) − (15 sq ft per window + 21 per door), then add waste. Vinyl squares = area ÷ 100 and boxes = squares ÷ 2. Fiber-cement planks = area ÷ 7 sq ft (12-ft plank at 7-in exposure). Wood lap lineal feet = area × 12 ÷ 6.5 (6½-in exposure).
Worked example: Walls of 120 ft × 10 ft with 10 windows and 2 doors: 1,200 gross − 192 openings = 1,008 sq ft net, 1,108.80 with 10% waste — 11.09 squares of vinyl (6 boxes), or 159 fiber-cement planks, or 2,048 lineal feet of wood lap.
When to use this
- Re-siding a house and building the order before the supplier visit.
- Checking a siding contractor's square count against your own wall measurements.
- Choosing between vinyl, fiber cement and wood with buy quantities side by side.
- Siding a garage, addition or gable end as its own small job.
How to use it, step by step
- Measure the total length of wall to cover and the wall height (add gable triangles into height).
- Count windows and doors — the estimator subtracts standard sizes.
- Pick the material to see its buy unit: squares/boxes, planks, or lineal feet.
- Set waste: 10% straight walls, up to 15% for gables and dormers.
- Order trim, starter and J-channel from the same perimeter with your supplier.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Wall length & height | Total run of wall and its height | Houses 100–160 ft × 9–12 ft |
| Windows / doors | Openings subtracted at 15 / 21 sq ft | Count every opening |
| Siding type | Sets the buy unit and coverage rate | Vinyl most common in the US |
| Waste % | Cutting around openings and gables | 10–15% |
Another worked example
A smaller ranch: 100 ft of wall, 9 ft high, 6 windows and 1 door, sided in fiber cement at 8% waste. Gross 900 sq ft minus 111 of openings leaves 789; with waste, 852.12 sq ft — 122 planks of 12-ft fiber cement at 7-in exposure, a one-weekend-two-people quantity.
Frequently asked questions
How much siding do I need for a 1,200 sq ft house?
Walls first, not floor area. A house with 120 ft of walls 10 ft high has 1,200 sq ft of gross wall; minus 10 windows and 2 doors (192 sq ft) leaves 1,008 sq ft, and with 10% waste that is 11.09 squares of vinyl — 6 boxes at 2 squares per box.
What is a square of siding?
The same unit as roofing: 100 sq ft of covered wall. Siding quotes, vinyl boxes and most price lists are all built on squares, which keeps siding comparable across materials.
Do I subtract windows and doors?
Yes — at standard sizes (about 15 sq ft a window, 21 a door) the subtraction is honest, because cutting around openings generates the waste the allowance then covers. Skipping the subtraction over-orders by roughly the same amount on a typical house.
How many fiber-cement planks cover a wall?
A 12-ft plank at 7-in exposure covers 7 sq ft. The default walls above (1,108.8 sq ft with waste) need 159 planks. Drop the exposure to 6 in for a shadow-line look and each plank covers only 6 sq ft — the count climbs to 185.
What waste percentage is right?
Ten percent for long straight walls; 12–15% for gables, dormers and short choppy elevations where every course ends in a cut. Pros order the extra and return unopened boxes.
🖌️ Painting the inside of those walls?
Once the outside is measured, the Paint Coverage Calculator turns room dimensions into gallons — coats and ceiling included.
How much does it cost to side an average house?
Material for the default house here (11.09 squares) runs roughly $1,100–$2,200 in vinyl, $2,800–$4,500 in fiber cement, before labour — installed totals commonly land at 2–3× material. The estimator's squares are the number every one of those quotes is built on.
What about the old siding underneath?
Vinyl sometimes goes over sound existing siding with furring and fanfold insulation; fiber cement and wood want a flat, nailed-to-stud substrate, so tear-off is typical. Disposal adds a dumpster to the budget, not squares to the order.