Why Beam Size Matters
Wood beams carry roof, floor, deck, and wall loads across open spans. A beam must resist bending, shear, and deflection at the same time. A deeper member usually controls deflection better. A wider or built up member often improves bending, shear, and bearing. This calculator checks all four limits with one form.
What The Calculator Evaluates
The tool uses span, tributary width, live load, dead load, optional point load, member size, species, grade values, and adjustment factors. It converts area loads into a line load. Then it estimates bending moment, support reaction, shear stress, bending stress, and total deflection. It also checks bearing pressure at the support.
Why Adjustment Factors Matter
Wood design values change with moisture, load duration, repetitive use, notches, and service conditions. Dry interior framing can often use stronger values than wet exterior framing. Short duration roof snow or wind effects may allow a higher bending value. The form includes practical factors, so advanced users can test more realistic cases.
Common Inputs
For floor beams, enter the floor tributary width. For deck beams, enter the joist span carried by that beam. For roof beams, include snow or roof live load when required. Enter point loads from posts, girders, or concentrated reactions separately. Keep units consistent. Use conservative assumptions when unsure.
Reading The Results
A ratio below one means the selected beam passes that check. A ratio above one means the beam is overstressed or too flexible. The highest ratio is the governing limit. A beam can pass bending but fail deflection. It can also pass stress but crush at the bearing plate. Review each line before choosing a size.
Practical Use
Use the suggested depth as a planning guide. Increase depth first when deflection is high. Add plies when bending, shear, or bearing controls. Confirm actual lumber dimensions before ordering. Built up beams need proper fastening between plies. Support posts, hangers, anchors, and foundations must also be checked.
Safety Note
This page gives preliminary sizing only. It does not replace local code, grade stamps, engineering judgment, or inspection. Loads vary by building use, snow region, wind zone, seismic area, and construction details. Always have a qualified professional review final beam sizes before construction.