Siding Calculator
By Taro Schenker | Updated February 11, 2026
Quick Answer: To calculate siding, use Squares = (Wall Area + Gable Area - Openings) x (1 + Waste%) / 100. One siding square = 100 sq ft. Deduct 21 sq ft per door and 9-21 sq ft per window. Gable area = 0.5 x base x gable height. Weight per square: vinyl 60 lbs, fiber cement 250, wood lap 150, engineered wood 175, aluminum 45. Add 10% for standard waste. For a house with 2,000 sq ft of wall area minus openings, you need roughly 20 squares.
Calculate how much siding you need for your home exterior. Enter your wall dimensions, choose a siding material, and get the exact number of squares, total weight, and estimated cost for your project.
How to Calculate Siding
The formula for calculating siding squares is:
- Measure the length and height of each exterior wall in feet.
- Multiply length by height to get the rectangular wall area.
- Add gable area if applicable (0.5 x base x gable height).
- Subtract openings: doors (21 sq ft each) and windows (9-21 sq ft each).
- Add your waste factor (10% is standard).
- Divide by 100 to convert square feet to siding squares.
Siding Material Comparison
Compare popular siding materials by cost, weight, lifespan, and maintenance requirements:
| Type | Cost / Square | Weight / Square | Lifespan | Maintenance |
|---|---|---|---|---|
| Vinyl | $150 - $250 | 60 lbs | 20 - 40 years | Low |
| Fiber Cement | $350 - $500 | 250 lbs | 30 - 50 years | Low |
| Wood Lap | $300 - $400 | 150 lbs | 15 - 30 years | High |
| Engineered Wood | $250 - $350 | 175 lbs | 20 - 30 years | Medium |
| Aluminum | $200 - $300 | 45 lbs | 30 - 50 years | Low |
Understanding Siding Squares
In the siding industry, materials are sold and priced by the "square." One square equals 100 square feet of siding coverage. This standard unit simplifies ordering and cost estimation for both contractors and homeowners.
For example, a wall that is 40 feet long and 9 feet tall has 360 square feet of area, which equals 3.6 squares. After subtracting windows and doors and adding waste, you can determine your exact order quantity.
Most siding products are packaged to cover 1 or 2 squares per box or bundle. Always round up to the nearest whole box when ordering to ensure you have enough material to complete the job.
Formula Summary
Siding Squares Formula: To calculate the number of siding squares, add the wall area and gable area, subtract openings, apply the waste factor, and divide by 100.
$$\text{Squares} = \frac{(A_{\text{walls}} + A_{\text{gables}} - A_{\text{openings}}) \times (1 + W\%)}{100}$$
Whole House Wall Area: $$A_{\text{walls}} = 2(W_1 + W_2) \times H$$
Gable Area: $$A_{\text{gable}} = 2 \times \frac{1}{2} \times W_2 \times H_g$$ (whole house) or $$\frac{1}{2} \times W \times H_g$$ (single wall)
Openings: $$A_{\text{openings}} = N_{\text{doors}} \times 21 + N_{\text{windows}} \times S_w$$
Weight: $$W_{\text{lbs}} = \text{Squares} \times \rho_{\text{lbs/sq}}$$
| Siding Type | Weight per Square (lbs) |
|---|---|
| Vinyl | 60 |
| Fiber Cement | 250 |
| Wood Lap | 150 |
| Engineered Wood | 175 |
| Aluminum | 45 |
Standard Assumptions: 1 siding square = 100 sq ft. Default waste factor is 10%. Door opening is 21 sq ft (3x7 ft). Window sizes: small 9 sq ft, medium 15 sq ft, large 21 sq ft. Gable area is calculated as a triangle (0.5 x base x gable height). Default pricing: vinyl $150, fiber cement $350, wood lap $300, engineered wood $250, aluminum $200 per square.
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- Plywood Calculator — calculate plywood sheets for sheathing and subfloors
Estimates are for planning purposes only. Consult a qualified contractor for critical projects. Actual material requirements may vary based on site conditions, waste, and installation methods.
Pricing last verified: February 2026. Material prices vary by region, season, and supplier. Prices shown are national averages for planning purposes.