Siding Square Calculator
Convert contractor-quoted siding squares to square feet and whole supplier boxes. Check openings, waste, leftover box coverage and material quotes by square versus box.
Enter measurements below. The result updates as you type.
Calculation breakdown
Area source
Known gross area is used directly.
Siding squares
One siding trade square is always 100 sq ft. Required squares may be fractional: the supplier decides how material is actually packaged.
Net area
850 - 50 = 800 sq ft
Boxes
880 sq ft ÷ 200 sq ft per box, rounded up to 5 complete boxes. Overbuy from packaging: 120 sq ft.
Compare quote bases
Per-square quote = fractional waste-adjusted trade squares × entered unit rate. Box quote = whole supplier boxes × entered box price, plus entered delivery. They are different sale units; confirm identical product, inclusions and supplier terms.
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Formula explanation
Core siding square estimate basis
Quoted gross siding sq ft = trade squares × 100. Net area = gross area − openings. With-waste siding squares = net sq ft × (1 + waste%) ÷ 100. Whole boxes = ceil(net sq ft × (1 + waste%) ÷ actual box coverage sq ft); surplus coverage = purchased boxes × box coverage − waste-adjusted required sq ft.
- The calculator shows exact fractional trade squares, net measured square footage and the optional whole-square reference; whole squares are not automatically purchase packages.
- Supplier rate per trade square is multiplied by fractional waste-adjusted squares; supplier rate per carton is multiplied by rounded whole-box count and optionally entered freight.
- Package counts round up only after waste is applied; optional remaining coverage refers to theoretical usable coverage, not a guarantee about cutting losses.
- Metric area inputs convert to square feet for the invariant 100 sq ft trade square; switching units does not change the number of boxes ordered.
Worked example
Known area example
850 sq ft known area, 50 sq ft openings, 10% waste, 200 sq ft per box
- 1Subtract openings from known area.
- 2Apply the waste allowance.
- 3Divide by 100 for siding squares.
- 4Divide by box coverage and round up.
Purchase area: 880 square feet, or 8.8 siding squares and 5 boxes at 200 square feet each.
Estimate assumptions
Check these assumptions before ordering
- One siding trade square equals 100 square feet of coverage, or approximately 9.29 square metres; a trade square is not necessarily an individual box.
- Quoted squares are treated as gross measured siding area before entered openings and additional waste.
- Fractional trade-square requirements are displayed without automatically rounding to the next square; actual unopened box quantities round by entered net box coverage.
- Known-area mode expects area before waste.
- Openings are deducted before waste and package rounding.
- Box or bundle net coverage must come from the exact product label; a generic 200-square-foot starting value is not a claim that every vinyl or fiber-cement package covers two trade squares.
- Material cost per trade square applies to the measured waste-adjusted area, while the box quote applies to whole boxes and optionally entered delivery; both exclude tax, installation and trim.
Measurement checklist
How to measure
- Use gross known-area mode when another takeoff already produced measured siding square footage, or set opening deductions to zero if it is already net.
- If the contractor gave you 8.5 siding squares, use quoted-squares mode to convert that gross quantity to 850 square feet without prematurely rounding it.
- Use wall mode for a single rectangular wall.
- Add window and door deductions as total opening area.
- Read actual net installed coverage per full package on the supplier carton: box or bundle area may differ dramatically by profile and manufacturer.
Avoid these errors
Common mistakes
- Confusing the trade area unit with an unopened box: 8.8 squares means 880 square feet, not 9 cartons.
- Comparing cost per trade square against cost per unopened box without accounting for package overage, delivery and whether the offers cover identical materials.
- Leaving default box coverage when the selected product covers a different area.
- Using this simple converter for a whole house with multiple gables and wall sections.
Estimate disclaimer
Verify before ordering.
Use the output as a planning baseline. Site conditions, product coverage, waste, supplier units, installation method, and local requirements can change the final quantity.
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Published guides
Understand the measurements and assumptions
Supporting guide
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Common questions
Use the result with context
01What is a siding square?+
A siding square is 100 square feet of siding coverage. The calculator converts purchase area into that siding trade unit.
02Should I enter net area or gross area?+
Enter gross siding area if you want the calculator to subtract openings, or enter net area with openings set to zero.
03How many square feet are in one square of siding?+
Exactly 100 square feet, approximately 9.29 square metres. A siding square is the contractor's area-based quantity, not a guaranteed manufacturer's unopened carton size. For example, 8.5 trade squares represent 850 square feet before any separate opening or waste adjustments.
04How do I convert a contractor's siding square quote into boxes?+
Enter the quoted squares as gross measured trade squares, subtract only measured openings that are not already deducted, choose a waste allowance, and enter the actual net coverage printed on a supplier package. Divide the adjusted area by that package coverage and round up whole cartons. Do not assume one square equals one box.
05Why does buying five boxes sometimes leave extra siding coverage?+
Five boxes each covering 200 square feet provide a nominal 1,000 square feet. If the waste-adjusted requirement is 880 square feet, whole unopened boxes add 120 square feet of theoretical surplus coverage. The surplus may not be reusable after real installation cuts and damage.
06How should I compare siding material quotes per square and per box?+
Enter supplier-confirmed material price per trade square and a separate price per whole package for the same product. The square basis multiplies the waste-adjusted fractional squares; the box basis rounds up to full packages and adds any entered box delivery fee. They are not necessarily equivalent contracts, and labor, tax, trim and included delivery must be checked before choosing.
07Why does box coverage matter?+
Box and bundle coverage varies by material, profile, and packaging, so the package count should use the coverage for the product you plan to buy.