Timber Post Bearing Area Calculator

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Imperial · sales tax

Axial Load

The compressive axial load the post transfers into the beam below it.

The load arriving at the BOTTOM of the post, which includes the post's own weight and anything landing on it part-way down. Perpendicular-to-grain bearing is usually what governs a timber connection long before the post's own compression does, so this number decides whether a bearing plate is needed — and a post that bears on an unsupported span of beam rather than over a support is a different problem again.

Allowable Bearing Stress Fc-perp

The species/grade's allowable compression stress perpendicular to grain, from the NDS design values.

NDS Fc-perp runs about 2.9-4.3 MPa (425-625 psi) for common softwood species.

Required bearing area

20.67 in²

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How this was calculated

Formula source(s)

Required bearing area = axial load ÷ allowable compression stress perpendicular to grain (Fc-perp), the standard NDS timber bearing check

Inputs used

Axial Load: 8.99 kip
Allowable Bearing Stress Fc-perp: 435.11 psi

Final result20.67 in²

What this calculation does not cover

The Fc-perp figure is used exactly as typed and no NDS adjustment factors are applied to it. The bearing area factor Cb, which raises the allowable value in the form (bearing length + 9.5 mm) divided by bearing length for bearings under about 150 mm long set back at least about 75 mm from the end of the member, is not credited, and the wet service and temperature reductions are not taken off either. Enter a value already adjusted for the edition and service conditions you are designing to.
Tabulated Fc-perp is governed by a deformation limit of roughly 1 mm (0.04 in) of indentation in the standard test, not by fibre rupture. Meeting the required area therefore controls how far the joint beds down, and exceeding it produces progressive crushing and a settling floor rather than a sudden collapse. Creep is not modelled at all, and perpendicular-to-grain deformation under sustained load keeps growing well beyond the initial value.
The output is a single area, not a bearing length, a plate size or a post section, and it assumes that whole area is loaded uniformly. Area cannot be won by spreading past the edge of the supporting member, and a thin plate that cantilevers beyond the post face does not deliver uniform stress unless it is stiff enough in bending, which is a separate check. An out-of-plumb, cupped or partially seated bearing contacts over only part of the face and sees a peak stress well above load divided by area.
Only crushing of the supporting member at one interface is checked. The post's own capacity in compression parallel to grain with the column stability factor CP, the supporting beam's bending and shear under the concentrated load, uplift and lateral restraint at the connection, and the same bearing check repeated at every interface further down the load path are all outside what this page computes.
Fc-perp from the NDS supplement is an allowable stress, so the axial load entered must be an unfactored service load combination; putting a factored LRFD load such as 1.2D + 1.6L (0.42 gal) against it oversizes the bearing by roughly the load factor. Fc-perp is also one of the few timber design values the load duration factor does not adjust, so a short-duration wind or seismic case does not justify a higher allowable stress here.

Add the equipment this sizes

This result is a specification — 20.67 in² — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

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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 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations1

Required bearing area = axial load ÷ allowable compression stress perpendicular to grain (Fc-perp), the standard NDS timber bearing check

Cite this page

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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.

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Checking an Exposed Timber Beam

How to calculate timber post bearing area in 3 steps

Axial LoadThe compressive axial load the post transfers into the beam below it.

Allowable Bearing Stress Fc-perpThe species/grade's allowable compression stress perpendicular to grain, from the NDS design values.

Required bearing areaThe tool computes the required bearing area from those figures and shows the formula, its sources, and a confidence rating alongside it.

Axial Load	Required bearing area (in²)
4 kip	9.19
6 kip	13.8
8 kip	18.4
10 kip	23
12 kip	27.6
14 kip	32.2
16 kip	36.8

Axial Load

Required bearing area (in²)

4 kip

9.19

6 kip

13.8

8 kip

18.4

10 kip

12 kip

27.6

14 kip

32.2

16 kip

36.8

Frequently asked questions

Why is perpendicular-to-grain stress the governing check here, not parallel-to-grain?

Because where a post bears on top of a beam (or a beam bears on a sill plate), the load crosses the grain of the supporting member, and wood is significantly weaker in compression perpendicular to grain than parallel to grain. So Fc-perp of the supporting member typically governs the required bearing area.

What if the actual post cross-section is smaller than the required bearing area?

Then a bearing plate, larger post, or a cap block with a wider footprint is needed to spread the load over enough area to keep bearing stress within the allowable Fc-perp. Bearing directly with an undersized post can crush the fibers of the supporting member over time.

Does the supporting member's species affect the allowable bearing stress?

Yes — Fc-perp values vary by wood species and grade and are published in the NDS supplement design value tables; always use the actual allowable value for the specific supporting member's species and grade rather than a generic assumption.