Beam Load Calculator Formula
Understand the math behind the beam load calculator. Each variable explained with a worked example.
Formulas Used
Total Load
total_load_psf = total_psfLoad per Linear Foot
load_per_ft = load_per_linftTotal Beam Load
total_beam_load = load_per_linft * spanReaction per Support (uniform)
reaction_per_support = load_per_linft * span / 2Variables
| Variable | Description | Default |
|---|---|---|
span | Beam Span(feet) | 16 |
tributary_width | Tributary Width(feet) | 8 |
dead_load | Dead Load (floor/roof weight)(psf) | 15 |
live_load | Live Load(psf) | 40 |
total_psf | Derived value= dead_load + live_load | calculated |
load_per_linft | Derived value= total_psf * tributary_width | calculated |
How It Works
How to Calculate Beam Loading
Formula
Load per Linear Foot = (Dead Load + Live Load) × Tributary Width
Total Load = Load per Linear Foot × Span
Support Reaction = Total Load / 2 (for a uniformly loaded simple beam)
Tributary width is the distance from the beam centerline to the midpoint between the beam and the next parallel support on each side. This calculation assumes a uniformly distributed load on a simply supported beam.
Worked Example
A 16 ft beam with 8 ft tributary width, 15 psf dead load, 40 psf live load.
- 01Total load = 15 + 40 = 55 psf
- 02Load per linear foot = 55 × 8 = 440 lbs/ft
- 03Total beam load = 440 × 16 = 7,040 lbs
- 04Reaction per support = 7,040 / 2 = 3,520 lbs
Frequently Asked Questions
What is tributary width?
Tributary width (or tributary area width) is the distance that a beam supports, measured perpendicular to the beam. It extends halfway to the next support on each side.
What is a typical residential floor live load?
40 psf for living areas and bedrooms. 100 psf for decks with public access. 20 psf for roof live loads (varies by location). These are minimum code requirements.
How do I size a beam from these loads?
Beam sizing requires calculating required section modulus based on bending moment (M = wL²/8 for uniform load). Consult an engineer or span tables for actual beam selection.
Learn More
Guide
How to Calculate Beam Load Capacity
Learn how to calculate beam load capacity using bending moment, section modulus, and material yield strength. Step-by-step engineering guide with formulas.
Ready to run the numbers?
Open Beam Load Calculator