The Wall Header Calculator checks whether a wood header or beam over an opening can carry a uniform load, by comparing its bending stress, shear stress and deflection with allowable values.
It treats the header as a simply supported beam: bending moment M = wL² ÷ 8, shear V = wL ÷ 2, and deflection δ = 5wL⁴ ÷ (384EI). You enter the span, the load, the beam’s actual size and the adjusted design values for your lumber, and the calculator reports each check as pass or fail.
Wall Header & Beam Calculator
Check a wood header or load-bearing wall beam for bending, shear and deflection under a uniform load.
Formula
- Bending stress: fb = M ÷ S, with M = wL² ÷ 8 and S = bd² ÷ 6
- Shear stress: fv = 1.5V ÷ (bd), with V = wL ÷ 2
- Deflection: δ = 5wL⁴ ÷ (384EI), with I = bd³ ÷ 12
- Checks: fb ≤ Fb′, fv ≤ Fv′, δ ≤ L ÷ limit
Where w = uniform load per foot, L = clear span, b and d = actual width and depth, E = modulus of elasticity, Fb′ and Fv′ = adjusted allowable stresses.
How the Calculation Works
Step 1: Calculate the maximum moment and shear for a uniform load on a simple span.
Step 2: Divide by the section properties of the beam to get the actual stresses.
Step 3: Compare stresses and deflection with the allowable values you entered.
Variables Explained
| Input | Meaning | Unit |
|---|---|---|
| Clear span | Distance between supports | ft, m |
| Uniform load | Total load on the header per foot | plf, kN/m |
| Beam width, depth | Actual (not nominal) size; two 2×10s = 3 × 9¼ in | in, mm |
| Fb′, Fv′, E | Adjusted design values for your species and grade | psi, MPa |
| Deflection limit | L/240, L/360 or L/480 | — |
Example Calculation
Given: 6 ft span, 400 plf, double 2×10 (3 × 9.25 in), Fb′ = 1,000 psi, Fv′ = 180 psi, E = 1,600,000 psi, L/360
M = 400 × 6² ÷ 8 = 1,800 ft·lb; S = 3 × 9.25² ÷ 6 ≈ 42.8 in³
fb ≈ 21,600 ÷ 42.8 ≈ 505 psi (≤ 1,000 OK)
fv = 1.5 × 1,200 ÷ (3 × 9.25) ≈ 65 psi (≤ 180 OK)
δ ≈ 0.037 in (≤ 72 ÷ 360 = 0.2 in OK)
Result: passes all three checks
Engineering Assumptions
- Simply supported, uniformly loaded beam; point loads are not modeled.
- The shear check is simplified (at the support); bearing length, lateral stability and code load combinations are not checked.
- You must supply adjusted design values; they depend on species, grade, size, moisture and load duration.
Headers in load-bearing walls should be sized from code span tables or verified by a qualified professional.
Formula Variations
A point load P at midspan uses M = PL ÷ 4 and δ = PL³ ÷ (48EI). Engineered lumber (LVL, glulam) uses the manufacturer’s design values.
Units and Dimensions
Keep units consistent: the calculator accepts ft/in with psi and plf, or metric units with MPa and kN/m, and converts internally. Deflection is shown in inches by default.
Frequently Asked Questions
How do I know what size header I need?
Check the bending, shear and deflection of a trial size against allowable values, or use your local code’s header span tables.
What load should I enter?
The total uniform load on the header per foot from the roof, floors and walls above; this depends on your building and should come from load calculations.
What is L/360?
A deflection limit: the beam may sag no more than its span divided by 360.
Why use actual dimensions?
A nominal 2×10 measures about 1½ × 9¼ in; stresses depend on the real size.
Does passing mean the header is code compliant?
Not by itself — other checks and code requirements also apply.