Beam Span Calculator
Span sketch from depth × factor or L/d — not structural design. Click any i for detail.
Span rule of thumb
Mode
i
Mode
Depth×factor or L/d ratio. |
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|---|---|
Depth (in)
i
Depth
Member depth in inches. |
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Factor
i
Factor
Joist-style rule: span_ft ≈ depth_in × factor. |
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L/d ratio
i
L/d
Span inches = depth × (L/d); result in feet. |
How to use this calculator
- Choose depth×factor or L/d mode.
- Enter member depth.
- Set factor or L/d.
- Treat the span as a rough sketch — use span tables/engineering for real loads.
Results explained
Builders sometimes sketch joist spans as depth(in) × a factor (feet), or from an L/d deflection-style ratio. Species, grade, spacing, load, and code govern real design — this page is educational only.
Quick reference: span sketches
rule: span_ft ≈ depth_in × factor; L/d: span_ft = depth×(L/d)/12.
| Item | Detail |
|---|---|
| 2×10 ~9.25 in | Common joist depth |
| Factor 1.5 | Rough educational default |
| L/d 360 | Common deflection sketch |
| Span tables | Authoritative for design |
Not a structural calculation — consult an engineer / code tables.
How the estimate is built
rule: spanFt = depth×factor; ld: spanFt = depth×ld/12.
Example scenario
9.25 in × 1.5 → about 13.9 ft sketch.
FAQ
Is this code-compliant?
No — use span tables and a qualified designer.
Steel beams?
Different methods — not covered.
Cantilevers?
Not modeled.
See lumber page?
For board-foot purchasing math.