Beam Depth Calculator
Enter the beam span and type (main/secondary/cantilever) to estimate the recommended beam depth and width from common span-to-depth ratios.
Input Data
Results
At a glance:Beam depth is governed by deflection (stiffness), using the empirical span/depth ratio: main beam about 12–15, secondary about 15–18, cantilever about 8–10. Recommended depth = span (mm) ÷ ratio; width is commonly 1/2–1/3 of depth. This calculator uses 12 (main), 15 (secondary), 8 (cantilever) for quick estimates. Actual dimensions must match loads, reinforcement and code deflection limits per a structural engineer.
Formula
Recommended depth = span (mm) ÷ span-to-depth ratio
Recommended width ≈ depth ÷ 2
$$h = \frac{L_{mm}}{r}$$$$b \approx \frac{h}{2}$$How to Use
- Enter the beam span (m).
- Select the beam type (main/secondary/cantilever).
- The tool outputs the suggested depth and width.
Case Studies
Residential main beam
Span 6 m, main beam.
Suggested depth 500 mm, width about 250 mm.
Office secondary beam
Span 4.5 m, secondary beam.
Suggested depth 300 mm, width about 150 mm.
FAQ
What is the span-to-depth ratio?
The ratio of span to beam depth. A smaller ratio (deeper beam) gives greater stiffness and less deflection; main beams carry more load so they use a smaller ratio.
Can this replace structural calculation?
No. This is a preliminary rules-of-thumb size; final dimensions must be verified by a registered structural engineer against loads and codes.
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References
Content review: Calculatorism Construction Team. Results are for reference only; please refer to the relevant authorities for the official figures.