Beam Load Calculator
Plan your structural engineering project with our free beam load calculator. Get precise measurements, material lists, and budgets.
Reviewed by Abdullah, Technical Content Specialist
Formula
Total Load (plf) = (Dead Load psf + Live Load psf) x Tributary Width + Beam Weight
Multiply the floor dead load and live load (psf) each by the tributary width to convert to pounds per linear foot. Add the beam self-weight in plf. For the maximum moment of a simply supported beam with uniform load, use M = wL^2/8. For LRFD, apply the combination 1.2D + 1.6L to the factored loads.
Worked Examples
Example 1: Residential Floor Beam
Problem:Size a beam supporting 20 psf dead load and 40 psf live load over a 12-ft tributary width with 20-ft span. Beam self-weight is 26 plf.
Solution:Dead load = 20 x 12 + 26 = 266 plf\nLive load = 40 x 12 = 480 plf\nTotal = 746 plf\nTotal on beam = 746 x 20 = 14,920 lbs\nMax moment = 746 x 20^2 / 8 = 37,300 lb-ft\nLRFD = 1.2(266) + 1.6(480) = 1,087 plf
Result:746 plf total, 37.30 kip-ft moment, 7,460 lbs reaction
Example 2: Commercial Roof Beam
Problem:Roof beam with 15 psf dead load, 20 psf live load, 16-ft tributary, 24-ft span, 35 plf beam.
Solution:Dead load = 15 x 16 + 35 = 275 plf\nLive load = 20 x 16 = 320 plf\nTotal = 595 plf\nMax moment = 595 x 24^2 / 8 = 42,840 lb-ft\nReaction = 595 x 24 / 2 = 7,140 lbs
Result:595 plf total, 42.84 kip-ft moment
Frequently Asked Questions
How do I calculate the load on a beam?
Beam load is calculated by multiplying the floor load (in psf) by the tributary width that the beam supports. The tributary width is the distance between the midpoints of the bays on either side of the beam. For example, if a beam supports joists spanning 6 feet on each side, the tributary width is 12 feet. A 40 psf live load times 12 ft tributary width equals 480 plf (pounds per linear foot). Add the dead load calculated the same way, plus the beam self-weight, for the total load.
What is the difference between LRFD and ASD load combinations?
LRFD (Load and Resistance Factor Design) multiplies loads by factors greater than 1.0 and resistance by factors less than 1.0. The primary combination is 1.2D + 1.6L, which amplifies dead load by 20 percent and live load by 60 percent. ASD (Allowable Stress Design) uses unfactored loads but divides the material strength by a safety factor. Both methods achieve similar safety levels but LRFD better accounts for the different reliability of dead versus live load predictions. LRFD is now the preferred method in AISC steel design.
How do I calculate the load-bearing capacity of a beam?
Beam capacity depends on material, cross-section dimensions, span length, and support conditions. For a simple rectangular wood beam, bending strength = (F_b x b x d^2) / 6, where F_b is allowable stress, b is width, and d is depth. Always consult a structural engineer for critical applications.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy