Siding Calculator

1. Measure each wall's width and its height from the foundation to the eaves. Width times height for each.
2. Measure each gable: the width at the eaves and the height from the eaves to the peak. A gable is a triangle, so it is half the width times the height.
3. Count the windows and doors and take their area out. A 3 x 4 ft window is 12 sq ft; a 16 x 7 ft garage door is 112.
4. Divide by 100 for squares, then add extra for cuts and laps: about 10 percent on a plain house, more with lots of gables, dormers, or corners.

Some estimators skip small windows and use the leftover as their waste. The calculator subtracts every opening and adds the waste on top, so the extra is a number you choose.

Vinyl comes in cartons by coverage. One maker's double 4 in carton holds 24 panels, 200 sq ft (2 squares), and weighs 89 lb. Panel lengths differ, so read the coverage on the box.

Fiber cement lap siding is sold by the plank. An 8-1/4 in HardiePlank 12 ft long, laid with 7 in showing, covers 7 sq ft and weighs about 20 lb, so a square is about 14.3 planks and 286 lb. For wood, engineered wood, or other lap siding, pick "Other" and enter the exposure and length.

Outside and inside corners run the full wall height at every corner. J-channel goes around each window (four sides) and door (three sides) and up both rakes of every gable. Starter strip runs along the bottom of every wall. The calculator adds up the feet of each and turns them into pieces at the trim length you set.

Enter your price per carton or plank and per trim piece; the ticket totals the order and gives a cost per square. The defaults are examples only. Siding contractors also quote per square, so the per-square number is the easiest one to compare, but theirs includes labor, house wrap, and flashing.

Fiber cement is heavy and long. At about 20 lb a plank, a half-ton's 1,150 lb payload carries about 57 planks, and 12 ft planks stick out more than 4 ft from a short bed. Carry them flat and supported, since they snap if they sag. Vinyl is light; its cartons are the bulky part. Long loads of lumber go through the board foot calculator.

• Measure each wall as a rectangle, then each gable as a triangle: half the width times the height from the eaves to the peak.
• Siding is quoted in squares. One square is 100 sq ft of wall, so a 1,500 sq ft wall area is 15 squares before waste.
• Fiber cement planks are heavy and long. Twelve-foot planks stick out of a short pickup bed, so stack them flat on a trailer or get them delivered. (Home Depot product listing)
• Count the trim while you measure: every outside corner, inside corner, window, and door gets its own pieces.

• Measuring wall height to the roofline at the gable end and also adding the gable, counting it twice.
• Forgetting the gable rakes when counting J-channel.
• Assuming every carton is 2 squares. Panel length and profile change it.
• Using the plank width instead of the exposure. An 8-1/4 in plank only shows 7 in.