📐 Siding Square Foot Calculator
This tool delivers professional‑grade siding estimates combined with inferential statistics. Use direct measurements or upload a sample of wall lengths to obtain a confidence interval for the total siding area. Every result includes the formula, uncertainty quantification, and a visual representation.
🔧 Input parameters & sample data
📈 Results & confidence interval
▼ total area with CI (shaded) — axis in sq ft
📋 reference tables
| Parameter | description | typical range |
|---|---|---|
| Number of walls | total walls to cover (population size) | 1–50 |
| Height / length | wall height and either direct length or sample lengths | 2–30 ft (0.6–9 m) |
| Waste factor | extra material for cuts & overlap | 0–15% |
| Sample data | list of measured wall lengths (comma‑separated) | at least 2 values |
| Confidence level | probability that interval contains true mean | 90%, 95%, 99% |
| output | interpretation |
|---|---|
| Estimated total area | best‑estimate siding square feet (including waste) |
| Confidence interval | range that likely contains the true total area (if sample used) |
| Sample mean (length) | average length from your sample |
| Sample SD | standard deviation of sample lengths |
| component | formula |
|---|---|
| Area (direct) | (length × height × number of walls) × (1 + waste/100) |
| Mean length (sample) | ∑xᵢ / n |
| Sample SD | √[∑(xᵢ – x̄)²/(n‑1)] |
| CI for mean length | x̄ ± (t·s/√n) or x̄ ± (z·σ/√n) |
| CI for total area | CI(mean) × (walls × height × (1+waste/100)) |
| level | z‑score (approx) | meaning |
|---|---|---|
| 90% | 1.645 | if we repeated sampling, 90% of intervals would contain true value |
| 95% | 1.96 | industry standard for high confidence |
| 99% | 2.576 | wider interval, more certainty |
| metric value | multiply by | feet |
|---|---|---|
| 1 meter (length/height) | 3.28084 | 3.28084 ft |
| 1 m² (area) | 10.7639 | sq ft |
❓ frequently asked questions
How do I use the sample data for a more accurate estimate?
Enter a few measured wall lengths (at least two) separated by commas. The calculator will compute the mean length and its confidence interval, then multiply by the total number of walls and height to give a statistically sound total area with uncertainty.
What if I don’t have sample measurements?
Just fill in the “direct length per wall” field. The calculator will work in deterministic mode and no confidence interval will appear. You still get a professional siding area estimate with waste.
Can I switch between feet and meters?
Yes – the unit toggle at the top converts all length inputs and sample values. The final area is always displayed in square feet, the industry standard for siding.
Why do I see a confidence interval even with a small sample?
The calculator uses Student’s t‑distribution for samples with fewer than 30 points, which widens the interval to reflect the extra uncertainty. For larger samples the t‑values approach the normal z‑values.
What does the waste factor include?
Waste accounts for offcuts, overlaps, gable trims, and errors. 5–10% is typical for simple gables; 10–15% for complex roofs or many corners.
How is the optional population standard deviation used?
If you know the true σ (from historical data), enter it. Then the interval becomes a z‑interval (normal distribution) instead of t‑based. Leave blank to use the sample sd.
Use the Surface Feet Per Minute Calculator for quick SFM calculations, or explore the full Feet & Inches Measurement Calculator category to access all length and measurement tools.