Post calculator
Check timber post buckling according to DIN EN 1995 for one axial load case
Load
Design compression load acting on the post.
Used to derive the timber modification factor for compression.
Geometry
Use the governing buckling length, not just the clear height.
Post width. Smaller side often governs weak-axis buckling.
Post depth. Compare it with the width for the weak axis.
Material and use class
Sets compression strength and stiffness for the buckling check.
Changes timber design resistance through moisture exposure in service.
Timber posts, explained simply
A timber post carries vertical compression from the member above down into the support below. In many real projects, the critical limit is not crushing of the wood. It is loss of stability by buckling.
This free tool checks one straight timber post under one axial load. It uses the weaker axis automatically and gives you a fast first check for section size, effective length, and timber grade.
What a post is
A post, sometimes called a column, is a vertical member that moves load from top to bottom. A beam works mainly in bending. A post works mainly in compression.
The usual danger is not that the wood is crushed directly. A slender post often bends sideways first and becomes unstable. That is the buckling problem this tool is built around.
Where timber posts appear
- Carport posts carrying roof beams or purlins.
- Front posts under a patio roof or canopy.
- Pergola corner posts and intermediate posts.
- Entrance canopy supports near the facade.
- Interior timber supports in frames or wall replacements.
- Temporary shoring or simple scaffold-like timber supports.
Why timber posts work well
- Good load capacity for relatively low self-weight.
- Easy to cut, drill, connect, and adapt on site.
- Warm appearance in visible construction.
- Renewable material when sourced well.
- Often cost-effective for small and mid-sized structures.
The benefit only holds if the post is sized correctly. Long and slender posts need a stability check, not just a rough strength guess.
Key terms that matter
Buckling vs. crushing
A short, stocky post may fail by direct compression. A long, slender post often fails earlier by buckling sideways. The second case is more sudden and usually governs in light timber work.
Practical rule: the longer and thinner the post, the more likely buckling becomes the controlling check.
Effective length
Effective length is the governing buckling length, not just the visible built height. It depends on the support conditions at the top and bottom and on any reliable restraint along the member.
Section size
The section is the width and depth of the post. Common small-scale timber sizes are 10 x 10 cm, 12 x 12 cm, 14 x 14 cm, or larger. The smaller side often governs the weak-axis buckling resistance.
Timber strength class
Not all timber performs the same. The strength class sets the compression strength and stiffness used in the check.
- C24: common structural softwood for standard load-bearing work.
- GL24h: glulam with more uniform properties and good practical reserve.
- GL28h: stronger glulam for higher loads or tighter geometry.
When a proper check matters
- Posts above roughly 2.5 m deserve a closer look. Above roughly 3.5 m, a proper stability check is usually the safer route.
- High roof loads, multiple supported beams, or floor loads.
- Slender proportions where height-to-thickness moves near 20:1.
- Permit-relevant construction such as canopies or extensions.
- Situations where people stand, walk, or gather below.
Typical starting sizes
These are rough starting values for C24 posts. They are not a final design. Real load, effective length, restraint, and timber grade can move the required section quickly.
| Height | Typical section | Typical use |
|---|---|---|
| up to 2.5 m | 10 x 10 cm | light pergola, fence-like support |
| 2.5 - 3.0 m | 12 x 12 cm | carport, patio roof |
| 3.0 - 3.5 m | 14 x 14 cm | taller canopy, higher open roof |
| above 3.5 m | 16 x 16 cm+ | larger roofs, hall-like structures |
Treat these values as orientation only. The tool result matters more than the table once you know the actual axial load and effective length.
Common mistakes to avoid
- Choosing the section too small because the load looks modest.
- Using wet timber that will twist, shrink, or move in service.
- Ignoring moisture protection near the base and connection zone.
- Assuming the base is stiff without checking the anchorage.
- Forgetting how the beam reaction is actually introduced into the post.
Full timber workflow: from roof beam to foundation
A post rarely stands alone. In a real project, one structural check leads into the next. Beam reactions move into posts, and post loads move into foundations.
Example: carport workflow
- Single-span beam calculator
Start with the roof beam or purlin. This gives you the support reactions that later reach the posts. - Post calculator
Use this step to check the vertical timber posts for compression and buckling under those reactions. - Foundation calculator
Use the final step to size the concrete footing from soil capacity and post load.
Practical order: start with the beam. Its reactions often define the loads for the following checks.