Fiber-Cement Siding Corner Post Calculator

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Who is doing the work?

Waste is set to 5% by hand. Pick a tier above to replace it, or keep your own figure.

Number of Corners

The total number of outside and inside corners to be trimmed.

Count every corner (outside and inside) along the sided walls that will receive a corner post.

Wall Height

The height each corner post must span.

Measure from the bottom of the siding to the top of the wall, since each corner post typically runs the full height of the corner in one piece.

Waste Allowance (%)

Extra material to allow for cut waste.

5% is typical for straightforward corners; increase it for taller walls that require spliced post lengths.

Corner post material needed

42 ft

High confidence

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

Total corner post length = number of corners × wall height × (1 + waste allowance), since each corner needs a full-height post piece

Inputs used

Number of Corners: 4
Wall Height: 10 ft
Waste Allowance (%): 5

Final result42 ft

What this calculation does not cover

Outside and inside corners are not the same purchase. A one-piece outside corner is its own product, an outside corner built from trim boards takes two lengths per corner rather than one, and inside corners are usually a smaller section. The metre total can be right while the order for each type is wrong.
Metres do not convert into sticks. A corner post wants to be one continuous piece, so a 2.7 m corner still consumes a whole 3.66 m (12 ft) length and the offcut does not carry to the next corner. Buy by the corner and treat this total as a cross-check on the metres, not as the quantity to order.
One height is applied to every corner. Gable-end corners run up to the rake, corners over a water table or band board start higher, and a two-storey corner needs a splice. Enter the eave height and the tall corners come up short by exactly the amount nobody measured.

Estimated cost — your price

Price per ft ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Schematic, drawn to the proportions you entered — not to scale on screen.

Part of a bigger job

This trade is one line of a job takeoff. Run the whole job and every other trade comes back with it, off the same measurements.

Fibre cement siding Check a quote
also measuresFiber-Cement Siding Plank Reveal & Course Fiber-Cement Siding Cutting Waste Factor Lap Siding Fastener Schedule Fiber-Cement Siding Caulk Joint Volume

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations1

Total corner post length = number of corners × wall height × (1 + waste allowance), since each corner needs a full-height post piece

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To hang siding or cladding and cut fibre-cement board. Generic types, no brands, no prices.

Protection this work requires

Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
Hardwood dust is a recognised carcinogen: extract at the tool and wear a P2/N95 respirator when cutting or sanding indoors.
Saws, grinders and breakers run above 85 dB, where hearing damage accumulates and does not recover: defenders or plugs for every cut, not just the long ones.
Most fatal falls on small jobs are from under three metres: use a tower or a ladder tied at the top, and never work off the top two rungs.

Show the 9 tools this job needs

Essential

Chalk line
Circular saw
Combination or framing square
Cordless drill/driver
Dust extractor or vacuum with a fine filter
Spirit level
Tape measure
Tower scaffold or trestles

Recommended

Mitre saw

Also needed as materials: chalk refill, circular saw blades, drill and driver bits, mitre saw blades.

what each cladding tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Installing Fibre Cement Claddinguses this calculator

Fibre cement will not forgive a flexed sheet, a blunt blade, a crushed nail head or a drifted reveal — a field guide built around those limits.

How to calculate fiber-cement siding corner post in 4 steps

Number of CornersThe total number of outside and inside corners to be trimmed.

Wall HeightThe height each corner post must span.

Waste Allowance (%)Extra material to allow for cut waste.

Corner post material neededThe tool computes the corner post material needed from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

Why does each corner need a full-height post?

A corner post conceals and protects the cut edges of siding panels at every outside or inside corner, so it runs the full height of the wall at that corner in a single continuous piece wherever possible.

Does this include both outside and inside corners?

Yes — enter the total count of every corner (outside and inside) that will be trimmed with a corner post; the calculation treats each one the same way.

How do I count the corners on a house?

Walk the whole outline, bump-outs and chimney chases included, and count outside and inside corners separately. On a plan where every wall meets at a right angle, outside corners always number exactly four more than inside ones: four and none on a plain rectangle, five and one on an L, six and two on a T or a U. Counts that do not differ by four mean a corner was missed. Then leave out any corner the siding never reaches, and enter the rest.

Why does one face of an outside corner look wider than the other?

A corner built from two trim boards has one board lapping over the edge of the other, so the face that shows that edge reads wider by a full board thickness. Where both faces should read the same, rip the board on that face narrower by the trim's thickness before it goes up.

When would I need more waste allowance than 5%?

Taller walls that exceed a single corner post's stock length require spliced pieces, which produces more cut-offs — increase the waste allowance accordingly for tall walls or multi-story corners.

Do the corner posts go up before the planks?

Yes. Corner boards, like the rest of the trim, go up first and the field planks butt into them. The gap left at that junction is a working joint to be sealed, not a tolerance to be closed up tight, so the planks are cut to leave it rather than forced against the board.

Corner boards or metal corners?

They are not interchangeable, and the choice belongs before the layout rather than when the first course reaches the corner. A corner board takes the planks butted against it with a sealed gap, which forgives a wall a little out of plumb. A proprietary metal or moulded corner fits each course on its own, so both elevations must bring every course to the corner at exactly the same height — possible only when both were laid out from one datum. This page counts corner boards by length; metal corners are counted per course, per corner.