James Hardie Siding Calculator
Work out how much James Hardie fiber cement siding your house needs — enter the perimeter, wall height and gable ends to get the squares to order after openings and waste, plus a material cost at Hardie prices rather than vinyl ones.
United States — national average · 2026 prices
Material only unless stated as installed. Excludes tax, permits and local labour. Verify with local suppliers — see how we calculate.
How this calculator works
Every figure above comes from the formula below, applied to the assumptions listed. Nothing is looked up from a hidden table — you can reproduce the result by hand.
Formula
wall area = perimeter × wall height
gable area = gables × ½ × gable width × gable rise
net = (wall + gable area) × (1 − openings% ÷ 100)
order = net × (1 + waste ÷ 100) · squares = order ÷ 100
Assumptions & limits
- Material price defaults to $4.50 per sq ft, the middle of the HardiePlank range (roughly $3–$6.50 depending on primed versus ColorPlus factory finish). That is materially above the $3 vinyl default on the base calculator.
- Fiber cement is sold in fixed 12 ft planks and butt-jointed over a stud, so offcuts are less reusable than vinyl. On a house with many corners and openings, 12–15% waste is more realistic than the 10% default.
- Installed cost runs about $6–$13 per sq ft. The gap over vinyl is labour, not just material: the board is roughly two and a half times heavier, is cut with shears or a dust-collecting saw rather than a standard blade, and is blind-nailed to studs.
- Trim and accessories are estimated at 20% of the siding, as on the base tool. HardieTrim, soffit and the required flashing details are priced separately by most suppliers.
- A "square" is 100 sq ft of siding, the unit the material is sold in.
- Gables are treated as triangles (half of width × rise). Hip roofs have no gables — set the count to zero.
- Openings default to a 10% deduction. For a tight bid, measure the real windows and doors instead of using the percentage.
- Default waste is 10%; complex walls with many corners and penetrations need more.
- Material price defaults to $3 per sq ft, mid-grade vinyl (real range roughly $2–$4.50). Fiber cement and engineered wood run higher. Accessories — starter strip, J-channel, corner posts — are estimated at 20% of the siding cost.
- Labor is excluded. Installed vinyl commonly runs $4–$8 per sq ft; installation standards are the manufacturer’s and the VSI certification program’s territory.
Worked example
The same 140 ft perimeter, 9 ft walls and two 30 × 8 ft gables, but in HardiePlank at $4.50/sq ft with 12% waste
- Wall + gable area = 1,260 + 240 = 1,500 sq ft
- After 10% openings = 1,350 · with 12% waste = 1,512 sq ft
- Squares = 15.1 · material = 1,512 × $4.50 = $6,804
- Trim and accessories at 20% ≈ $1,361
Result:About 15.1 squares — roughly $7,300 to $9,800 in board and accessories, or $9,000 to $19,500 installed.
Built and maintained by Christoph Ballmer, Honeygoat GmbH
Method and constants last checked against the calculator code on August 25, 2026. Independent trade review is not yet in place for this calculator — see how we handle review.
Read the site-wide calculation methodology · estimate vs. quote and safety limits
What makes James Hardie different to estimate
James Hardie fiber cement is a cement, sand and cellulose board: it does not melt, it does not feed termites, and it holds paint far longer than wood. What that buys in exchange is weight and difficulty — a Hardie plank weighs roughly two and a half times a vinyl one, it has to be cut with a shears or a dust-collecting saw, and it is nailed rather than hung, so it takes a crew that has done it before.
The geometry is the same as any siding — perimeter times wall height, plus the gable triangles, minus openings, plus waste — but two of the numbers change. The price opens at $4.5 per square foot rather than the $3 the base calculator assumes for mid-grade vinyl. And the waste opens at 12% rather than 10%, because fiber cement comes in fixed 12 ft planks that are butt-jointed over a stud, so offcuts are less reusable than vinyl trimmed to fit.
squares = (perimeter × height + gables × ½ × width × rise) × (1 − openings%) × (1 + waste%) ÷ 100
Fiber cement against the alternatives
| Siding | Material $/sq ft | Installed $/sq ft | Typical life |
|---|---|---|---|
| Vinyl, mid-grade | $2.00–$4.50 | $4–$8 | 20–30 yr |
| Engineered wood | $3.00–$6.00 | $5–$12 | 20–30 yr |
| James Hardie fiber cement | $3.00–$6.50 | $6–$13 | 30–50 yr |
The premium over vinyl is mostly labour, not board. Fiber cement weighs roughly two and a half times as much, has to be cut with shears or a dust-collecting saw because cutting it releases respirable crystalline silica, and is nailed to studs rather than hung on a nailing hem. That is also the honest answer to whether it is a DIY job: the cutting and the flashing details are where inexperienced installs fail, and where the warranty is lost.
Related planning
For vinyl, engineered wood or a general estimate, use the siding calculator. The sheathing behind the siding is sized by the plywood calculator, and if the roof is being done in the same season, the roof replacement cost calculator budgets that half of the envelope.
Frequently asked questions
How do I calculate how much Hardie siding I need?
The same way as any siding: perimeter times wall height, plus the gable triangles, minus about 10% for openings, plus 10% waste, divided by 100 for squares. What changes with Hardie is the waste number. Fiber cement planks come in fixed 12 ft lengths and are butt-jointed over a stud, so offcuts are less reusable than vinyl - many installers plan 12 to 15% rather than 10% on a house with many corners and windows. Set the waste field above to match your wall layout.
How much does Hardie board siding cost?
Material runs roughly $3 to $6.50 per square foot for HardiePlank lap siding, with ColorPlus factory finish at the upper end and primed board at the lower. Installed, expect about $6 to $13 per square foot - meaningfully above vinyl, because the board is heavier, cut slower and nailed rather than hung. On a 1,500 sq ft wall area that is roughly $9,000 to $19,500 installed.
Should I buy ColorPlus or primed Hardie?
ColorPlus arrives with a baked-on factory finish and a finish warranty; primed board arrives ready for a painter. ColorPlus costs more per square foot and saves a full paint cycle plus the site time, which usually makes it the cheaper choice on a whole-house job. Primed wins when you want a colour outside the range, when you are siding a small area, or when a painter is already on site for trim and windows.
What is HZ5 and HZ10, and which do I need?
They are the two climate-engineered product lines. HZ5 is made for freeze-thaw climates - the northern half of the country - with a formulation that resists moisture movement and seasonal swelling. HZ10 is for hot, humid and coastal conditions, engineered against heat, sun and moisture. The right one is decided by where the house is, not by preference, and using the wrong line can affect the warranty. Your supplier stocks the one for your region.
Can I install Hardie siding myself?
Physically yes, and it is where most DIY siding jobs go wrong. Cutting fiber cement releases respirable crystalline silica, so it needs shears or a saw with dust collection and proper respiratory protection - not a standard circular saw in the open. Boards are heavy enough to want two people, blind nailing has to hit the studs, and the joint, clearance and flashing details are specified by the manufacturer rather than left to judgement. Getting those details wrong is what voids the warranty.
How much siding does a 2,000 sq ft house need?
Floor area alone cannot answer this - the wall area depends on the shape. A single-story 2,000 sq ft house might have a 180 ft perimeter and 9 ft walls (about 16-18 squares with gables), while a two-story house with a 130 ft perimeter and 18 ft of wall carries 23-26 squares. Measure the perimeter and heights and let the calculator above do the rest.