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Siding Calculator

Wall and gable area minus openings, siding squares with waste, and vinyl boxes.

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Don't subtract small windows

Siding pros often ignore openings smaller than about 20 sq ft, because the panel pieces cut out around them are rarely usable elsewhere. Subtract garage doors and big picture windows, but treat small bathroom windows as solid wall and your estimate will land closer to what you actually use.

How to estimate siding

Measure around the outside of the house and multiply by the wall height from the bottom of the siding to the eaves: wall area = perimeter × height. Each gable end is a triangle, so add ½ × base width × height to the peak for each one.

Subtract the area of doors, windows and garage doors, then add a waste allowance. Siding is sold in squares of 100 sq ft. The Vinyl Siding Institute's installation manual and most manufacturers recommend about 10% extra for cutting around openings and corners, more on houses with many gables or bump-outs.

Most double-4 and double-5 vinyl siding panels ship two squares to a carton, which is what the box count assumes. Trim pieces such as J-channel, starter strip, inside and outside corner posts, and soffit are sold separately by the piece; measure around each opening and along each corner for those.

Where these numbers come from

The formulas and default values in this calculator are based on:

  • Vinyl Siding Institute Vinyl Siding Installation Manual
  • manufacturer carton coverage for double-4 and double-5 vinyl panels (typically 200 sq ft per box)

These are planning estimates. Check product labels, your local building code, and a licensed contractor before you buy materials or build.

Frequently asked questions

How do I measure a gable end?

Measure the width of the wall at the eave line, then the height from that line to the peak. Multiply them and divide by two. If you can't reach the peak, count siding courses on a neighboring wall to estimate height, or use the roof pitch.

Is fiber cement figured the same way?

Yes for area and squares. Fiber cement planks are sold by the piece rather than the box, so divide the square footage by the exposed face of each plank (for example 7 in. exposure on a 12 ft plank covers 7 sq ft).

Why add waste if I'm subtracting openings?

Panels are a fixed length, so every run ends with an offcut, and corners and openings need precise cuts. Waste covers those cuts plus a few spare panels for future repairs.

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