Wood Beam Calculator
Bending and deflection checks for sawn dimension lumber — simply supported, uniform load, with the NDS adjustment factors applied in the open. Answer in five seconds; every step spelled out below.
Design values from the NDS 2018 Supplement tables · No account required
The full calculation, spelled out
Below is the live CalcPackage editor in public view — the same worksheet an engineer would stamp: reference design values, the C_D and C_F adjustment chain, section properties from dressed dimensions, and both pass/fail checks in sequence.
Change any input — every dependent block recomputes. Click ✦ Explain on any block and the AI walks you through the engineering, including why a deeper member takes a size-factor penalty.
With a free account you get full authoring control: add repetitive-member factors, switch load durations, or build your own worksheet from scratch. You can change any number — sign up free to change the math.
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How this calculator works
The calculator checks a simply supported sawn-lumber beam under uniform dead and live load using allowable stress design per NDS 2018. Reference design values F_b and E come from the NDS 2018 Supplement (Table 4A; Table 4D for Southern Pine), keyed to species and grade. The applied bending stress f_b = M/S — with S computed from dressed (not nominal) dimensions per Table 1A — is compared against the adjusted design value F_b′ = C_D·C_F·F_b, with C_D = 1.0 for occupancy live load and the size factor C_F from Table 4A. Live-load deflection 5wL⁴/384EI is checked against the IBC L/360 limit.
Assumptions and limitations
Simply supported single span, uniform load, visually graded dimension lumber (2–4 in. nominal thickness), dry service, normal temperature, single member (C_M = C_t = C_r = 1.0), and a continuously braced compression edge (C_L = 1.0). Shear, bearing, built-up members, and other load durations are covered in the full editor templates. This calculator is a design aid — engineering judgment and final responsibility rest with the licensed engineer of record.
Frequently asked questions
Why are the section properties smaller than b×d from the size name?
A nominal 2x10 is actually 1.5 × 9.25 inches after surfacing. The worksheet computes S and I from the dressed dimensions per NDS Supplement Table 1A — using nominal dimensions is the most common error in hand calcs.
Is the calculation verified?
Yes. Every value is matched against the NDS 2018 Supplement tables and dimension-checked on every recomputation. The chain-of-custody rail on the right of the editor records the verification history.
What about snow load or repetitive members?
The full editor handles C_D for other load durations, the repetitive-member factor C_r, wet service, and beam stability — start from this worksheet with a free account and extend it.