Construction
Beam Span Rough Calculator
Get a very rough beam depth guide from span length. This is not a structural design.
The result is only a rough depth guide in millimetres for early planning, not a finished beam size, so a licensed engineer must still design the real beam.
Formula
Rough depth guide = span in millimetres divided by 20. This is a rule-of-thumb starting point only, not a design calculation.
How it works
Enter the distance the beam must span. The guide divides span by twenty to suggest an approximate depth for early planning. Loads, material, supports and deflection all change the real answer, so a licensed engineer must design any beam that carries real load.
Worked example
For example, a beam span of 4 metres is 4000 millimetres, and 4000 divided by 20 is 200, so the rough depth guide is about 200 mm.
FAQs
Can I build from this guide?
No. This is only for early planning and budgeting. Real beams need a proper structural design.
Why span divided by twenty?
It is a common rough rule for initial sizing. Different beam types and loads use different ratios.
What else affects beam size?
Load, material, support conditions, deflection limits and local codes all matter, which is why professional design is required.
Rough estimate only — consult a licensed professional for structural work before building. Structural work must be designed by a licensed professional.
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