Hardie® Siding Calculator
This calculator estimates board and carton quantities for Hardie®-style fiber cement lap siding using editable, typical dimensions. It is not affiliated with, endorsed by, or a substitute for James Hardie's own product specifications.
Project type
Wall measurements
Enter each wall's length and height in feet and inches. Wall area = length × height.
Gable ends
No gables added. Gable area = base × rise ÷ 2.
Windows & doors
No openings added. Each opening's area is subtracted from your gross siding area.
Siding material
Waste factor
Waste accounts for cuts at corners and openings, gable angles, damaged pieces, and pattern matching. 10% is a common starting point for a simple rectangular home; complex roof lines or diagonal cuts often need more.
Trim & accessories
Actual accessory requirements vary by installation method and manufacturer — use these as a starting checklist, not a final order.
08Cost estimateOptional
Applied to area including waste — what you'll actually buy.
Applied to net wall area — what installers actually cover, before waste.
Enter your own prices for the most accurate estimate for your area. Leave fields blank or at 0 to exclude them.
Preview
Estimated siding needed
Net area
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Waste added
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Total area (w/ waste)
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Siding squares
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James Hardie units
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Est. total cost
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How we calculated this
Trim & accessories
Want professional installation?
Bring this estimate to local siding contractors when comparing quotes, or reach out with questions.
Contact usHow it's calculated
- 1. Net siding area = gross wall and gable area minus openings.
- 2. Required area = net area plus your waste allowance (12% is a common starting point for fiber cement).
- 3. Carton coverage defaults to 175 sq ft (25 boards at a 7 in exposure) — edit this to match your exact product line.
- 4. Cartons needed = required area ÷ carton coverage, rounded up.
Worked example
A home with 1,450 sq ft of net wall area and a 12% waste factor:
| Net area | 1,450 sq ft |
| Plus 12% waste | +174 sq ft |
| Required area | 1,624 sq ft |
| Siding squares | 16.24 squares |
| Cartons to order | 10 cartons (≈250 boards) |
Actual Hardie® product dimensions (HardiePlank®, HardiePanel®, etc.) vary by line — confirm exact coverage with your supplier.
Assumptions
- • This is an independent estimating tool and does not use James Hardie’s proprietary specifications or pricing.
- • Board and carton dimensions are editable defaults, not a guarantee of any specific Hardie® product line’s coverage.
- • Always confirm exact board dimensions, exposure, and installation requirements with the manufacturer or a certified installer.
Tips
- • Different Hardie® product lines (plank, panel, shingle-style) have different coverage — check the specific product’s spec sheet.
- • Factory-primed boards still typically need field painting of cut edges per manufacturer instructions.
Choosing between Hardie®-style product lines and finishes
“Hardie” covers more than one product. Lap boards (sold as HardiePlank®), vertical panels (HardiePanel®) and shingle-style pieces all have different coverage, and this is why the calculator’s board length and exposure are editable. Pick the line first, then enter its dimensions from the spec sheet. Don’t reuse a lap-board exposure for a panel product. The Hardie and fiber cement calculation guide walks through a full example.
You’ll also choose between a primed finish that gets painted on site and a factory-applied finish. Primed boards are cheaper up front but need to be painted on site, which adds a labor step, and the manufacturer’s instructions say how soon and how (check the current guide and warranty terms). Factory-finished boards cost more and cut down on painting, but you’ll need touch-up paint for every cut. Order it with the boards so the color and sheen match. Whichever you use, protect cut edges as the manufacturer instructs.
Because the material is fiber cement, cutting matters. Manufacturers call for dust control when cutting, and a lot of installers cut outdoors with dust-reducing tools and respiratory protection. Check the current safety guidance for your product before the crew starts. If you’re asking contractors for quotes, ask whether they are trained on the specific line and whether the quote includes the manufacturer’s required flashing and fasteners. Typical prices are on the Hardie board siding cost page.
This page is independent and is not affiliated with James Hardie.
This is a planning estimate
Frequently asked questions
Is this an official James Hardie calculator?
No. This is an independent estimating tool that uses editable, typical fiber cement dimensions. It is not affiliated with or endorsed by James Hardie.
How do I get an exact quantity for HardiePlank®?
Enter your specific board length and exposure in the "Siding material" section — these values vary by product line and should be confirmed on the manufacturer’s spec sheet.
What waste factor should I use?
Fiber cement installers commonly use 10–15% waste to account for cutting and occasional breakage.
Is primed or pre-finished Hardie®-style siding a better choice?
Primed boards lower the material cost but add a paint step on site. Pre-finished boards reduce on-site painting. Which is better depends on your budget, color plans and how much touch-up you’re comfortable with.
Should I get extra boards for cut-outs and corners?
The waste factor covers this. Fiber cement installers commonly use 10–15%; go higher for houses with lots of corners and dormers.
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