Concrete Beam Calculator — ft, yd³, rebar

How to Calculate Concrete for Beams

Choose the section type, enter beam width, total depth and clear span in feet and inches, then set the number of beams and a waste allowance (5% for simple work, 10% typical, 15% for congested formwork or pump loss). The tool returns volume in yd³, ft³ or 60/80 lb bag count, plus self-weight at 150 lb/ft³ for crane and shoring checks. For one-off beams, the concrete volume calculator or the bag mix calculator may be quicker; for vertical members use the concrete column calculator.

Reinforcement per ACI 318-19

Bottom tension bars carry positive bending; top compression/continuity bars are detailed at supports. Stirrups resist shear and confine the section — spaced as close as d/4 in plastic-hinge regions and d/2 in critical zones near supports, opening up at midspan per ACI 318-19 §18.6.4. The minimum flexural ratio is the greater of 3√f′c/fy and 200/fy (§9.6.1.2) — about ρ = 0.0033 for f′c = 4,000 psi and Grade 60 steel. Bar lengths include a 40·d_b compression lap (§25.5) and end hooks.

Formulas

Rectangular: V = b × h × L. T-beam / L-beam: V = b_w × h × L + (b_f − b_w) × h_f × L (stem plus flange above the stem). Self-weight = volume × 150 lb/ft³ (4,050 lb/yd³). Stirrup perimeter = 2(b_w − 2c) + 2(h − 2c) + hooks, with clear cover c = 1.5 in. Effective depth d = h − c − d_stirrup − d_bar/2.

FAQ

What is the typical beam depth? A practical rule for simply supported beams is span/16 to span/12, so a 20 ft span usually needs a 15–20 in deep section. Should I include the flange volume? The flange is normally cast monolithically with the slab; this tool adds the flange-above-stem portion to the total so material ordering covers the full pour. Estimating slab-on-grade or edge curbs instead? See the wall and curb & gutter calculators, or the concrete stairs calculator for stair stringers.

On pour day

Three line items estimators forget on beams. Short-load fee — a single 20 ft 12×18 beam is about 0.8 yd³; ready-mix plants charge $90–150 below their 3 yd³ minimum, so combine beam and slab pours or budget for the surcharge. Typical 2025 USA pricing is $160–210/yd³ for 4,000 psi mix, $0.90–1.30/lb for Grade 60 rebar, and $400–650/beam for forming + tying labor on residential work. Pump or crane — beams cast above grade or inside congested forms almost always need a pump truck ($800–1,400 minimum) — wheelbarrows do not work past 30 ft of hose. Cage tie-off — under ACI 318-19 §25.5 a 40·d_b lap on a #5 bar is 25 in, so a 22 ft beam needs one splice per bar — order 20 ft stock plus splice pieces, not "one long bar."