Hardie Siding Calculator
Estimate James Hardie plank boards, boxes and coverage for your house, with a fiber-cement cost range and full accessory takeoff.
Walls (feet)
Gables / triangles optional
Windows & doors to subtract
Tip: measure each wall's width × height at its widest points. A per-wall audit table appears below so you can check every number.
Your siding squares, panels and cost appear here.
Estimated from wall count and perimeter — confirm against your actual corners and openings.
Cost per sq ft: – · per square: –
| Surface | Area (sq ft) |
|---|
Estimating James Hardie fiber cement
James Hardie plank is sold by the piece and boxed by the piece, not simply by the square, so your board count depends on the plank length and the reveal (the exposed height of each course). Get those two things right and the rest is straightforward. This calculator assumes standard plank coverage and converts your measured wall area into boards and boxes, then flags the waste you should carry for cut-heavy elevations.
Because Hardie is heavier and cut differently from vinyl, plan a slightly higher waste factor and remember the accessories: trim boards, corners and flashing at openings. The tool lists those so your order is complete.
Step-by-step: from tape measure to order
The whole process is measure, subtract, pad, convert. Here's how that maps onto the fields above.
- Set your basics. Units and material at the top control everything downstream, so start there.
- Walls, one at a time. Enter width × height × quantity for each face of the house.
- Triangles and cut-outs. Add gable base and rise; subtract every significant window and door.
- Cushion and cost. Choose a waste percentage and, if you're budgeting, set labor and removal rates.
- Review the breakdown. Check the per-wall audit, then print or share.
Boards from area
With standard plank coverage of about 5.3 sq ft per board, a 1,900 sq ft net wall needs roughly:
- 1,900 × 1.10 waste ≈ 2,090 sq ft of coverage
- 2,090 ÷ 5.3 ≈ 395 boards
- At around 15 planks per box, about 27 boxes
Your reveal and plank length change the coverage — set them to match your product.
How reliable is this estimate?
Reliable enough to plan and shop with, and honest about its limits. The core arithmetic — area, openings, squares, waste — is exactly what an estimator or a building-supply desk uses, so the quantities are sound when your measurements are. The coverage and price defaults come from typical manufacturer specs and widely reported installed costs, not a single source, which is why we show ranges rather than false precision. Your final order should still be confirmed against a field measure and a real quote.
Beyond the board count: planning a Hardie install
Fiber cement rewards planning more than any other siding because it's heavy, pricey and awkward to return. Once you have boards and boxes, think through these before ordering.
- Cutting and dust: fiber cement needs a dust-reducing blade and, ideally, outdoor cutting with a mask. Factor the right blade into your tool budget.
- Fastening: use corrosion-resistant nails or screws per James Hardie's spec, blind-nailed or face-nailed depending on the product. The accessory list flags fasteners.
- Trim program: Hardie has a matching trim and corner system. Ordering trim in the same color batch keeps the whole elevation consistent.
- Painting: pre-finished (ColorPlus) skips field painting; primed boards need paint on all cut edges. Decide which before you order.
With those decided, the board and box figures above become a complete order you can hand to a lumberyard.
Frequently asked questions
How do I calculate how much Hardie siding I need?
How many square feet does a piece of HardiePlank cover?
How much waste should I add for Hardie?
Does the calculator include trim and corners?
Is James Hardie more expensive than vinyl?
What homeowners say
"The board-to-box conversion is what I needed. My lumberyard order matched the count exactly."
"Bumped waste to 12% for all my gables and it worked out perfectly."