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Header Size Calculator

Calculate header size — header size — bending-only section modulus and depth from span, load and allowable stress with waste for US projects. Enter dimensions, select units and add waste to get instant, supplier-ready numbers.

1. Measurements & Dimensions

HEADER SIZE CALCULATOR ESTIMATE
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Enter dimensions above to calculate

Calculation Breakdown & StepsFormula: Bending-only required section modulus S = wL² × 12 / (8 × allowable stress); rectangular depth = √(6S / breadth).
  1. Enter values to see step-by-step substitution.

    Engineering Assumptions:

    • Bending demand only for a simply supported rectangular section under uniform load. The output is not a recommended nominal lumber size.
    • Deflection, shear, bearing, stability, connections, built-up member action and local code requirements can govern. An engineer must complete the design.
    VISUAL GUIDE — HEADER SIZE CALCULATORframing · header-size-calculator

    TOP VIEW — Simply supported header span × Uniform line load (lb/ft)

    Header Size Calculator topSimply supported header span 14ftUniform line load (lb/ft)Header Size14×12 = 168 ft²

    SECTION — Adjusted allowable bending stress (psi) 4in

    Header Size Calculator sectionHeader Size 4in4"Bending-only required section modulus S = wL² × 12 / (8 × allowable stress); rectangular depth = √(6S / breadth). · +5% → 2.18 yd³
    Header Size Calculator — Bending-only required section modulus S = wL² × 12 / (8 × allowable stress); rectangular depth = √(6S / breadth). · example 14×12 @4in = 56.0 ft³ (2.07 yd³) → 2.18 yd³ with 5% waste · header-size-calculator

    What Is This Calculator?

    The Header Size Calculator — Frames US walls and floors — studs, joists, headers, beams and board feet.

    What Does It Calculate?

    • Stud count from spacing
    • Board feet (T x W x L /12)
    • Joist/beam loads with waste

    How to Use the Calculator

    1. Measure Wall 20 ft, studs 16 in OC — use feet for length/width and inches for thickness where typical.
    2. Enter values and select units. The calculator converts to feet before calculating (inches /12, yards x3).
    3. Adjust waste % and optional price, then click Calculate. Results show with waste included.
    4. Use Reset to clear and try another size.

    Formula & Engineering Methodology

    Bending-only required section modulus S = wL² × 12 / (8 × allowable stress); rectangular depth = √(6S / breadth).

    • Spacing — 16 or 24 in on-center
    • Board — Thickness*Width*Length/12

    All units convert to exact standard engineering dimensions (NIST SP 811) before calculation to ensure consistency between US Customary and Metric measurements.

    Worked Example

    Example: Wall 20 ft, studs 16 in OC

    STEPVALUE
    Studsceil(20*12/16)+1 =16
    Board feet 2x4x81.5*3.5*96/144 =3.5 bf
    With waste18 studs

    Construction Information

    Material: Studs 2x4/2x6, 16 in o.c. typical. SPF #2, 1.5x3.5 in actual. Board foot = 1x12x12 in.

    Studs 16 in OC, 24 in non-load. Add cripples, headers per opening.

    Material Information

    Studs 2x4/2x6, 16 in o.c. typical. SPF #2, 1.5x3.5 in actual. Board foot = 1x12x12 in.

    Waste & Overages

    Add 10% for cuts and cripples — 15% for gable walls.

    Practical Tips

    • Add 1 stud per corner and opening
    • Crown joists up

    Common Mistakes

    • 16 in vs 24 in o.c. — count off 30%
    • Forgetting cripples under sills

    Assumptions & Engineering References

    • Bending demand only for a simply supported rectangular section under uniform load. The output is not a recommended nominal lumber size.
    • Deflection, shear, bearing, stability, connections, built-up member action and local code requirements can govern. An engineer must complete the design.

    This calculator provides an estimate based on your inputs. Actual requirements vary by site, material and installation. For code-regulated or load-bearing work, consult a qualified professional.

    Calculations run 100% in your browser — zero tracking of your dimensions or input data.

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    Frequently asked questions

    What does the Header Size Calculator calculate?

    The Header Size Calculator estimates header size quantity for US jobs — Stud count from spacing, Board feet (T x W x L /12), Joist/beam loads with waste. Enter dimensions, choose units, add waste and price to get instant results.

    How do I measure for header size?

    Measure wall 20 ft, studs 16 in oc on site. Use the unit selectors — the tool converts inches→feet (÷12) and yards→feet (×3) before math. For non-rectangular, split into rectangles and add.

    How much waste should I add?

    Add 10% for cuts and cripples — 15% for gable walls.

    How accurate is this header size estimate?

    Math is exact for your inputs. Actual needs vary by site, material and installation. For structural loads, have a qualified professional review your plans per code. Add 5–10% waste for rectangular, 10–15% for irregular.

    About Calculator Street

    Built by Vipul Otari for US homeowners & contractors. Calculator inputs are processed in your browser. Estimates depend on your measurements, product specifications and the assumptions shown on this page. Confirm order quantities with your supplier and structural requirements with your project designer. Page updated: 2026-09-11.

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