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The wood member's modulus of elasticity along the grain.
From the design values table for the species and grade you are actually using — it is a published property, not a measurement, and it varies by a factor of two across common structural species. Use the value the code table gives for the grade, including any adjustment the table requires for wet service or duration. Buckling capacity is directly proportional to it, so borrowing a softwood figure for a hardwood post, or the reverse, moves the answer by that whole factor.
The column's cross-sectional moment of inertia about the axis it will buckle around.
For a rectangular section, I = b×d³/12. Enter the value in millions of mm⁴ (e.g. a value of 100 means 100,000,000 mm⁴).
Accounts for how the column's ends are restrained against rotation and translation.
How the ends are HELD, which is the hardest thing to be honest about in a buckling check. A pinned-pinned column takes 1.0; fixed-fixed takes a smaller value and buckles at a higher load; a column free to sway at the top takes a value above 1.0 and buckles much sooner. Most real timber connections are closer to pinned than anyone would like, and assuming fixity a bolted joint does not deliver is the standard way a buckling check comes out optimistic.
The column's unsupported (unbraced) length between points of lateral restraint.
Between genuine points of restraint, which is not necessarily the column's full length — a post braced at mid-height in one direction has a different unbraced length each way, and the buckling check has to be run for the worse of them. Restraint means something that stops the column moving sideways there, so a horizontal member simply framing into it without being held itself is not a brace.
Critical buckling load
262.7 kips
They open the calculator with your figures already in it
Timber Column Euler Buckling Calculator: 263 kips — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Euler's critical buckling load formula: Pcr = π²EI/(KL)², where K is the effective length factor for the column's end conditions
Inputs used
- Modulus of Elasticity E
- 1595415.12 psi
- Moment of Inertia I (×10⁶ mm⁴)
- 100
- Effective Length Factor K
- 1.0 — pinned-pinned
- Unbraced Length
- 10 ft
What this calculation does not cover
- The calculation takes only the moment of inertia, never the cross-sectional area, so it cannot compare the Euler load with the load at which the wood simply crushes. At the default values the 1,206 kN (271,120 lbf) returned implies a section roughly 186 mm square, which at a compression-parallel-to-grain strength near 20 MPa crushes at about 690 kN (155,118 lbf). Stocky columns fail that way long before the Euler load is reached, and this page will not tell you when that is the case.
- The moment of inertia box has no unit selector: it stays in millions of mm⁴ even when the unit switch is set to imperial and the modulus is being read in psi. A 5½ × 5½ in post has I = 76.3 in⁴, which must be entered here as 31.7, because one in⁴ is 416,231 mm⁴. Entering the inch value directly overstates the buckling load by a factor of more than two.
- One run checks one buckling axis. A rectangular post has two moments of inertia and frequently two different unbraced lengths, because sheathing or noggins may restrain the weak axis at mid-height while the strong axis runs the full storey height, and the governing case is the largest (KL)²/I rather than automatically the smaller I. Run it once per axis and take the lower answer.
- Buckling is governed by stiffness, and design codes require a low-percentile modulus for stability checks — Emin in the NDS, E0,05 in Eurocode 5 — not the published mean value that the 11,000 MPa default represents. The size of that reduction is jurisdictional, but it is substantial, and sustained load reduces effective stiffness further through creep, which this page does not model at all.
- No factor of safety is applied. The figure is the load at which a perfectly straight, concentrically loaded elastic column collapses, and it carries no adjustment for load duration, moisture content or elevated temperature, so none of CD, CM and Ct in the NDS or kmod in Eurocode 5 appear in the arithmetic. A post with a beam framing to one face, or with the initial bow that graded timber is permitted to have, is also carrying bending, and that axial-plus-bending interaction is a separate check this page does not perform.
- The four effective length factors offered are Euler's textbook end conditions and assume ideal restraint. A base plate bolted to a slab is not the perfectly fixed end that K = 0.5 describes, design practice commonly recommends higher values than theory for exactly that reason, and a column free to sway at the top can exceed the K = 2.0 that the cantilever option allows.
Add the equipment this sizes
This result is a specification — 262.7 kips — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
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
- Euler's critical buckling load formula: Pcr = π²EI/(KL)², where K is the effective length factor for the column's end conditions
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