Siding Calculator

How to use the siding calculator

What this calculator does

This tool estimates the exterior surface area that must be covered with siding after subtracting doors and windows, then adds a user-selected waste allowance. It also converts the result into siding squares and multiplies the purchase area by a material price per square foot or square meter. It is a quantity and material-cost estimator, not a structural design, fastening schedule, moisture-control specification, labor quote, or permit check. For installation details and wall-system considerations, consult manufacturer instructions and qualified local professionals; HUD's Exterior Walls rehabilitation guide explains why cladding, drainage, and weather barriers must be considered as a system.

When to use it

Use the calculator while budgeting a single wall, comparing siding products with different prices, checking whether a contractor's material quantity is plausible, or preparing a shopping list before visiting a supplier. You can also switch to a triangular gable and estimate its face separately, then repeat the calculation for each distinct surface.

How to calculate

1. The calculator opens with a complete demonstration project and an immediately available example XLSX workbook. Review the first-open numbers to see how the inputs flow into the results.
2. Choose Surface shape and Measurement system. Replace the sample width, height, opening dimensions, counts, waste factor, and unit price with measured project values. Results update live.
3. Read Siding needed as the purchase-area target. Use Siding squares when a supplier quotes coverage in 100-square-foot units, and use the breakdown table to verify each subtraction and addition.
4. Select Download Excel to export the current validated inputs and outputs. Reset clears the demonstration data, results, and workbook state; Excel export remains disabled until a complete valid project is entered again.

Input guide

Surface shape is required. Choose Rectangular wall for width × height, or Triangular gable for one-half × width × peak height. Measurement system is required and converts all length fields plus the unit price; imperial uses feet and ft², while metric uses meters and m². NIST's explanation of area in square units is a useful reminder that length conversions must be squared when converting area.

Wall or gable width and Wall or gable height are required positive decimal lengths. The sample values are 28 ft and 10 ft. Larger dimensions increase gross area directly; a common mistake is entering inches while the control is set to feet. For a gable, height means the vertical distance from the base line to the peak, not the full wall height below it.

Number of doors and Number of windows are required whole numbers from zero upward. Their corresponding Door width, Door height, Window width, and Window height are required positive decimal lengths whenever the count is greater than zero. The startup example uses two 3 ft × 6.67 ft doors and six 3 ft × 4 ft windows. Increasing opening count or size reduces net siding area. Measure rough covered openings consistently and do not mix feet-and-inches notation such as 6'8" into a decimal-only field.

Waste factor is a required percentage from 0% through 100%; the sample uses 10%. It increases only the net area after openings are deducted. Straight, simple walls may need less, while complex layouts, pattern matching, fragile material, and future repairs may justify more. Unit price is a required nonnegative material price per ft² or m²; the sample is $4.50/ft². Enter the coverage-adjusted unit price, not the price of a carton unless you first divide the carton price by its stated coverage.

Output guide

Gross surface area is the wall rectangle or gable triangle before openings. Total opening area combines every door and window. Net area before waste is gross area minus openings and cannot be negative. Waste allowance is the added area produced by the selected percentage. Siding needed is net area plus waste and is the main purchase target. Siding squares is an exact conversion of the purchase area into 100-ft² units in imperial mode; in metric mode it still reports the equivalent trade squares for comparison. Estimated material cost multiplies siding needed by unit price and excludes labor, trim, fasteners, delivery, tax, house wrap, insulation, disposal, and equipment.

The Area and cost breakdown table lists Component, Count, Area per item, Total area, and Effect. “Subtracted” rows reduce coverage, “Added” is the waste allowance, and “Purchase target” is the final area. Zero openings are valid; a zero net area means the entered openings consume the entire surface and no siding quantity is produced.

Worked example

The startup wall is 28 ft × 10 ft, so gross area is 280.00 ft². Two doors at 3 ft × 6.67 ft subtract 40.02 ft². Six windows at 3 ft × 4 ft subtract 72.00 ft². Net area is therefore 280.00 – 40.02 – 72.00 = 167.98 ft². A 10% waste factor adds 16.798 ft², giving 184.778 ft², displayed as 184.78 ft². Dividing by 100 gives 1.85 siding squares. At $4.50 per ft², estimated material cost is 184.778 × $4.50 = $831.50 after display rounding.