Calculate estimated beam deflection, span-to-deflection ratio, reactions, shear, and bending moment for a simply supported beam. Use this beam deflection calculator for floor beams, deck beams, roof beams, headers, girders, joists, and preliminary structural planning.
Uniform load:
The calculator uses the simply supported beam formula 5wL⁴ ÷ 384EI to estimate maximum deflection near midspan.
Center point load:
The calculator uses PL³ ÷ 48EI to estimate maximum deflection for a point load placed at the center of the span.
Combined load:
The calculator adds the uniform load deflection and center point load deflection together for a basic combined estimate.
Deflection ratio:
The calculator compares span length to deflection and shows a span ratio such as L/360 or L/480.
A beam deflection calculator helps estimate whether a beam may feel stiff enough or bend too much under load.
It can help compare beam span, load, stiffness, moment of inertia, estimated deflection, span ratio, reactions, shear, and bending moment before final design.
Your result shows estimated maximum deflection, allowable deflection, span ratio, load status, total load, support reactions, maximum shear, and maximum bending moment. These results are estimates for simple planning and do not replace structural design.
Beam deflection is the amount a beam bends or sags under load. It is usually measured in inches for residential and light commercial framing calculations.
L/360 means the allowable deflection is the beam span divided by 360. For a 12-foot span, L/360 equals 0.4 inches.
A shorter span, lighter load, higher modulus of elasticity, or larger moment of inertia can reduce deflection.
No. This calculator estimates deflection and simple reactions. Final beam sizing depends on strength, deflection, bearing, connections, load combinations, material grade, local code, and professional review.