Hardie Plank Siding Calculator
Estimate HardiePlank lap siding area, plank quantity, waste, squares and installed project cost.
Estimate HardiePlank-style lap siding quantity, 12-foot plank count, siding squares and a transparent installed-cost range from measured wall area, openings, exposure and waste.
Siding quantity and cost estimate
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Use this Hardie plank siding calculator to estimate how much lap siding you need from exterior wall area, openings, visible plank exposure and waste. It also provides an editable installed-cost range, which makes the same tool useful as a Hardie plank siding cost calculator without hiding local pricing assumptions inside the formula.
The quantity calculation is based on visible exposure, not the plank’s full face width. That distinction matters because the upper portion of lap siding is overlapped by the next course and does not add visible wall coverage.
Calculate Net Siding Area Before Counting Planks
Start with gross exterior wall area, then subtract windows, doors and other areas that will not receive siding. If you do not already know the wall area, the calculator can estimate rectangular wall area from exterior perimeter × average wall height and let you add gable area separately.
Floor area is not a dependable substitute for exterior siding area. Two homes with the same floor square footage can have very different wall areas because of stories, footprint shape, gables and additions.
HardiePlank Exposure and Coverage
James Hardie’s current Hardie Plank product page directs installers to product-specific technical documents and installation instructions. Published U.S. HardiePlank estimating guides use 12-foot planks and common width/exposure pairs such as 5¼-inch planks with 4-inch exposure, 6¼ with 5-inch exposure, 7¼ with 6-inch exposure, 8¼ with 7-inch exposure, 9¼ with 8-inch exposure, and 12-inch planks with 10¾-inch exposure.
The coverage formula is straightforward: coverage per plank = exposure in feet × plank length. A 12-foot plank with 7 inches of visible exposure covers 7 square feet before waste. The calculator uses the exact coverage and then rounds the final order up to a whole plank.
Add Waste for Cuts and Layout
Waste accounts for cutoffs, damaged pieces and layout losses. Ten percent is a common planning input, but simple uninterrupted walls may need less and cut-heavy elevations with many openings or gables may need more. The waste percentage affects order quantity and siding squares; it does not automatically inflate the installed $/sq-ft rate a second time.
Estimate Hardie Plank Siding Cost
Current 2026 cost guides vary because they include different combinations of labor, removal, trim, painting, weather-resistive barriers and project complexity. Angi currently reports Hardie board projects around $7 to $18 per square foot across its overall cost guidance, with lap-style ranges overlapping that band. Other national guides publish different totals depending on scope.
For that reason, the calculator exposes the base installed low and high rates as editable inputs. The default range is a national planning starting point, not a quote. The tool then shows transparent adjustments for stories, wall/access complexity and your local price factor.
Keep Removal, Trim and Painting Visible
Old-siding removal, trim, weather barrier work, field painting and permits can materially change a project. Rather than silently assuming those items are included in every published square-foot price, this calculator lets you enter them separately. This makes it easier to compare contractor bids that use different scopes.
If you are using a factory-finished product, do not automatically add a full field-painting allowance. If you are using primed siding that will be finished after installation, include the actual painting quote or a reasonable project allowance.
Installation Requirements Still Matter
A material takeoff does not replace the manufacturer’s installation instructions. James Hardie notes requirements involving starter strips, joint staggering, flashing and other installation details. Product availability, climate-zone formulation, approved fastening methods and exact dimensions can also vary. Verify the current technical documents for the product and region you are actually buying.
Frequently Asked Questions
How many square feet does one HardiePlank cover?
It depends on visible exposure and plank length. A 12-foot plank installed at 7-inch exposure covers 7 square feet. A 12-foot plank at 5-inch exposure covers 5 square feet.
How many Hardie planks do I need for 1,000 square feet?
At 7-inch exposure and 12-foot plank length, 1,000 square feet requires about 143 planks before waste. With 10% waste, the exact calculation is about 157.14 planks, so the order rounds up to 158 whole planks.
Should I subtract windows and doors?
Yes, if you are doing a detailed takeoff. Subtract areas that will not receive siding, then apply your waste factor to the remaining net siding area.
Does this calculator include HardieTrim?
It does not guess trim footage from the wall area. Use the trim allowance for a known quote or estimate because corner, window, door and architectural trim varies by design.
Is this an official James Hardie calculator?
No. SeriesCalculator is independent and is not affiliated with or endorsed by James Hardie. Verify final quantities and product requirements with current manufacturer documents and your supplier or installer.
Methodology and Sources
Product and installation context comes from James Hardie’s current Hardie Plank product and professional installation pages. Common U.S. exposure presets are based on published HardiePlank lap-siding estimating guides. The editable 2026 cost starting range is informed by current Angi and This Old House cost research. Published costs are planning references only and should be replaced with local pricing when available.