Beam Span Estimator
Preliminary rule-of-thumb span sizing
Rules of thumb used
| Element | Depth |
|---|---|
| Timber floor joist | L / 15 |
| Timber beam / girder | L / 12 |
| Steel beam (IPE) | L / 20 |
| Reinforced concrete beam | L / 12 |
| RC flat slab | L / 28 |
Suggested preliminary size
Depths are rounded up to common increments; widths are indicative proportions.
About Beam Span Estimator
The beam span estimator gives a preliminary size for a structural element from its clear span, using the span-to-depth ratios engineers rely on for early design. Pick the element type — timber floor joist, timber beam or girder, steel IPE beam, reinforced concrete beam, or RC flat slab — and enter the distance between supports.
Each element type has its own rule of thumb: floor structures need proportionally more depth than heavily loaded girders, and concrete behaves differently from steel or timber. The tool applies the matching ratio, rounds the depth up to a common commercial increment, and suggests an indicative width alongside a cross-section sketch.
This is scheme-design sizing — the kind of number an architect pencils in before the engineer runs the real calculation. It is useful for checking whether a floor build-up is plausible or a beam will fit in a ceiling zone, free and instant in your browser. Every structural element must ultimately be designed and verified by a qualified structural engineer.
How to use Beam Span Estimator
- Select the structural element: timber joist, timber beam, steel IPE beam, RC beam, or RC flat slab.
- Enter the clear span between supports, in meters.
- Read the suggested depth and indicative width, rounded to common sizes.
- Review the rules-of-thumb table to see which span-to-depth ratio was applied.