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Timber Post CalculatorTimber Post & Column Size Calculator

Size a timber post for a vertical load. Checks compression and buckling across standard post sizes in a clear pass/fail table, accounting for height, end fixity and timber grade.

Post Size TableCompression + BucklingEnd FixityPass/Fail ComparePDF Report
TP

Timber Post Calculator

Timber Post & Column Size Calculator

Load & Geometry
kN

Vertical compression on post. 1 kN ~ 102 kg.

mm
Timber
OK
Timber Post Results
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mm
Smallest Post
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kN
Capacity
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ratio
Slenderness
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grade
Strength Grade
Post SizeCapacitySlendernessResult
Post Calculation
About Timber Post Calculator
A timber post under vertical load can fail two ways: by crushing (compression) or by buckling sideways if it is too slender. This calculator checks a range of standard square post sizes against your load, height and end fixity, showing in a pass/fail table which sizes are safe and highlighting the smallest economical post. It combines compression capacity with Euler buckling theory.
Where Is This Used?
Post + Column SizingPergola + VerandaCarport StructuresDeck PostsMezzanine ColumnsStructural Estimating
Formulas Used
Effective length Le = K x Height (K by end condition)Slenderness = Le / radius of gyration (r = sqrt(I/A))Compression (squash) capacity = fc x AreaEuler buckling load Pcr = pi squared x E x I / Le squaredSafe if capacity >= load AND slenderness <= 180
Frequently Asked Questions
What is slenderness and why limit it?
Slenderness is the effective length divided by the post's radius of gyration - essentially how long and thin it is. Slender posts buckle sideways well before they crush, often suddenly. Codes cap slenderness (commonly around 180 for timber) so posts fail in a predictable, ductile way rather than buckling catastrophically.
How does end fixity change the result?
How a post is held at top and bottom changes its effective buckling length. Pinned-pinned uses the full height (K=1.0); fixing both ends shortens it (K=0.7), allowing a smaller post; a cantilever fixed only at the base doubles it (K=2.0), needing a much bigger post. Honest end-condition input is essential.
Can I build this from the calculator alone?
Use it to size and compare options - it applies the correct compression and buckling theory. But a real structure needs a qualified engineer to confirm against your code (IS 883, Eurocode 5), including load duration, moisture, eccentric loading, connections and lateral restraint that affect the true capacity.
ResourcesView the formulasFormula Library
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