Wood Beam Span Calculator (NDS Reference Check)
Construction & Home ImprovementCheck a wood beam against deflection, bending, and shear limits using NDS reference design values by species and grade.
Overall Result
Combined result across the deflection, bending, and shear checks.
Actual Deflection
0.102
Calculated deflection under the given load.
Allowable Deflection
0.333
Deflection limit based on the selected L over n ratio.
Actual Bending Stress
609.5
Calculated bending stress under the given load.
Allowable Bending Stress (Fb)
900
Reference allowable bending stress for the selected species and grade.
Actual Shear Stress
57.1
Calculated horizontal shear stress under the given load.
Allowable Shear Stress (Fv)
180
Reference allowable shear stress for the selected species and grade.
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Construction & Home Improvement calculators
Calculator Stats
Creators
Odeh Ahwal0people find this calculator helpful
Views
Helpful
Saved
Embeds
Construction & Home Improvement calculators
Frequently Asked Questions
What do the Pass and Fail results mean?
Each check compares the beam actual stress or deflection against an allowable reference value. Pass means the beam meets that specific check using the unadjusted reference design values for the selected species and grade; Fail means it does not, and a larger beam, shorter span, lighter load, or stronger species and grade would be needed.
Are these full NDS adjusted design values?
No. These are the base, unadjusted reference values from NDS design value tables for a No.2 structural grade. A complete code-compliant design also applies adjustment factors for load duration, moisture, temperature, repetitive-member use, and member size, which generally increase allowable capacity for typical dimension lumber. Because those factors are omitted here, this check tends to be conservative, understating real capacity rather than overstating it. This calculator does not replace a licensed structural engineer or a local building code review.
Why is the Southern Pine bending value different from other sources?
Southern Pine allowable bending stress decreases as the lumber gets larger under current NDS design value tables, so a value suited to a small 2 by 4 would overstate strength for a large beam. This calculator uses a conservative mid-range reference value intended to stay safe across common beam sizes rather than the higher small-member value.
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