How to calculate siding
Siding covers the rectangular walls of the house plus the triangular gables under the roof ends. Add those areas together, take out windows and doors, and add some extra for cuts. Divide by 100 to get squares.
Walls = total wall length × wall height
Gables = ½ × gable width × gable height × number of gables
Squares = (walls + gables − openings) × (1 + waste %) ÷ 100
Example: a house with 160 ft of wall at 9 ft high has 1,440 sq ft of wall. Two 30 ft wide gables that rise 7.5 ft add 225 sq ft. Taking out 12 windows (180 sq ft) and 2 doors (42 sq ft) leaves 1,443 sq ft. With 10% extra that's 1,587 sq ft, or about 15.9 squares.
Measuring your house
- Walk around the house with a tape or measuring wheel and add up the length of every wall you're siding.
- Measure wall height from the bottom of the siding line (usually just above the foundation) to the soffit.
- Measure each gable separately if they're different sizes, calculate them, and enter the average.
- Skip garage door and large patio door areas by counting them as several doors, or by subtracting their area from the wall length.
Trim and accessories
Siding panels are only part of the order. You'll also need starter strip along the bottom, J-channel around windows and doors, outside and inside corner posts, and soffit and fascia if you're replacing those too. Each is sold by the linear foot, so measure around openings and down every corner separately.
Frequently asked questions
What is a square of siding?
A square is 100 square feet of wall coverage. Siding is priced and ordered by the square, so a house with 1,800 square feet of wall needs 18 squares before waste.
How much extra siding should I order?
About 10 percent is typical for a simple house. Homes with many corners, gables, dormers or windows waste more in cuts, so 15 percent is safer there.
How do I measure a gable for siding?
Measure the gable's width at the base and its height from the base to the peak. A gable is a triangle, so its area is half the width times the height.
Should I subtract windows and doors?
Yes, for accurate numbers. The calculator subtracts about 15 square feet per window and 21 per door. Very small windows are often ignored, because the waste around them is similar to their area.
How many boxes of vinyl siding do I need?
Many vinyl siding boxes cover 2 squares (200 square feet), but box sizes vary by product. Divide the squares you need by the squares per box and round up.