Header Span Planning
A header carries weight above a wall opening. That opening may be a door, window, pass through, or framed bay. The span looks simple. The load path may not be simple. This calculator gives a clear math check before deeper design work starts.
Why Span Math Matters
A header bends under weight. It also shears near the supports. It may crush the bearing area below each end. It may deflect too much, even when bending stress looks acceptable. Good span math reviews every limit. The smallest safe value controls the answer.
Inputs That Affect Results
The opening width is the clear span between supports. Tributary width estimates how much floor, roof, or ceiling area sends load to the header. Dead load covers fixed material weight. Live load covers people, furniture, storage, or temporary use. Snow load can be included when roof framing bears on the header. A point load can represent a concentrated post or beam reaction.
Member Properties
The calculator uses total member width, depth, section modulus, moment of inertia, and area. More plies increase width. More depth usually helps bending and deflection more strongly. Material values control allowable bending, shear, stiffness, and bearing checks. The duration factor adjusts allowable bending when your design method permits it.
How to Read the Answer
A passing result means each selected check meets the entered limits. A failing result shows the weak item. The governing allowable span is the smallest calculated safe span. Use the safety factors to see which item is closest to its limit.
Example Decisions
Try several depths before choosing a header. A deeper member may reduce deflection quickly. Extra plies may help bearing and shear. Lower loads may allow a longer opening. Higher snow or storage loads may shorten it. Keep results with your project notes. Export the table when comparing sizes. Check that supports, posts, and footings can carry the same reactions safely. Never treat one number as final approval.
Use With Care
This page is a planning calculator, not a permit drawing. Local codes, load combinations, fasteners, notches, holes, lateral bracing, moisture, species, grade, and connection details can change the final design. For occupied buildings, use approved span tables or a licensed professional.