Concrete Column Calculator — ft, yd³, rebar

How to Calculate Concrete for Columns

Column volume is small but rich-mix work: tight forms, dense rebar cages, and a lot of vertical pumping or bucketing. This calculator sizes the concrete by cubic yard and by 60 lb or 80 lb bag, totals the cage steel per ACI 318-19, and prices ready-mix, bag mix, and labor so you can compare a small truck order against bagged mix for a handful of columns. A 5–10% waste allowance covers form leakage, the over-vibrated top, and pump-line priming; bump it toward 12–15% for tall slender forms or pier footings poured monolithically.

For the footing or pier under the column see the concrete volume calculator; size connecting grade beams and bearing walls separately, and if you are mixing on site the bag calculator converts the same volume to 60/80 lb bags and cost.

Reinforcement per ACI 318-19

Longitudinal steel must stay between 1% and 8% of the gross cross-section area Ag (§10.6.1) — the result flags an under- or over-reinforced cage instantly. Tied columns need at least 4 bars (6 for circular ties, more for spirals). Tie spacing is capped at the least of 16 longitudinal-bar diameters, 48 tie-bar diameters, and the smallest column dimension (§25.7.2); the default 8″ suits a #5 vertical with #3 ties. Vertical bar runs add a lap of 40 d_b in compression (the calculator switches to 60 d_b for tension or seismic splice classes) wherever the height exceeds a 20 ft stock length, plus a 2 ft allowance for dowel projection and standard hooks.

Formulas

Square: V = side² × H. Rectangular: V = b × h × H. Circular: V = π/4 × D² × H. Concrete self-weight at 150 lb/ft³ (4,050 lb/yd³). Tie perimeter = 2 × ((b − 2·cover) + (h − 2·cover)) + hook allowance, with 1.5 in clear cover; circular ties use π × (D − 2·cover). Bag yields: 80 lb ≈ 0.022 yd³ (0.6 ft³), 60 lb ≈ 0.017 yd³ (0.45 ft³).

FAQ

What is the minimum column size? ACI 318 sets no absolute minimum, but 10″×10″ is the practical floor for tied columns and 12″ diameter for spiral columns so the cage and aggregate fit with cover. How many bags per column? A 12″×12″×10 ft column is about 0.37 yd³ — roughly 17 bags of 80 lb or 22 bags of 60 lb mix; past three or four columns a short-load ready-mix order is usually cheaper than bags. Square vs. circular for the same size? A round column of diameter D holds π/4 ≈ 79% of the concrete of a D×D square, which the shape tabs let you compare directly. Sitting on a curb-and-gutter run, or supporting stair flights? Size those pieces separately.

On pour day

Three column-specific traps. Short-load fee — six 12×12×10 ft columns are ~2.2 yd³, well under the 3-yd³ minimum where most US plants kick in an $80–150 short-load charge, so the chip presets compare ready-mix at $170–220/yd³ for 4000 psi against 80-lb QUIKRETE at roughly $6.50/bag. Starter dowels and laps — vertical bars need a 40 d_b compression splice (60 d_b for tension or seismic Class B per ACI §25.5.2) wherever a 20 ft stock bar runs out; this calc already adds one lap above 20 ft of height plus a 2 ft hook/dowel allowance. Cage and pump — keep tie spacing at the lesser of 16 d_b·vert, 48 d_b·tie and the smallest column dimension (§25.7.2), and budget a pump or boom truck for anything past 30 ft of hose or above the first floor — typically $700–1,200 minimum in 2025 USA.