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.