Concrete Column Calculator — m, m³, rebar
How to use this calculator
Pick the column shape (square, rectangular, or circular), enter each dimension and choose its unit (m, cm, or mm) from the dropdown, then set the clear story height and how many identical columns you are pouring. The shape tabs auto-switch when you click a preset so you can compare a square tied cage against the round equivalent on the same footprint.
Cost — pick ready-mix per m³, 50 kg bags, or 25 kg bags. Select currency.
Reinforcement — vertical bars 12–25 mm with ties 8–10 mm, lap splices per EC2 §8.7, min/max steel ratios (0.2%–4% Ac per §9.5.2).
Labor — rate per column, per m³, or flat price.
Saved Calculations
| Time | Shape | Size | Qty | Vol m³ | Cost | Rebar | Rebar | Labor | Total |
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How to Calculate Concrete for Columns (Metric)
Column volumes are small but the work is mix-heavy: tight formwork, a dense cage, and a lot of vertical placing. This calculator sizes the concrete in m³ and by 25 kg or 50 kg bag, totals the cage steel to EN 1992-1-1, and prices ready-mix, bag mix, and labour in your chosen currency so you can weigh a small truck order against bagged mix for a few columns. A 5–10% waste allowance covers form leakage, the over-vibrated top, and pump priming; raise it to 12–15% for tall slender forms or columns cast monolithically with a pad footing.
Size the pad or pier beneath the column with the concrete volume calculator; design connecting grade beams and bearing walls separately, and for hand-batched mixes the bag calculator converts the same volume to 25/50 kg bags and cost.
Reinforcement per EN 1992-1-1 (Eurocode 2)
Longitudinal steel must stay between 0.2% and 4% of the gross cross-section area Ac (§9.5.2) — the result flags an under- or over-reinforced cage at once; many National Annexes also require As,min ≥ 0.10·NEd/fyd. A rectangular column needs at least 4 bars, a circular one at least 6. Link spacing scl,tmax is the least of 20× the smallest longitudinal-bar diameter, the lesser column dimension, and 400 mm (§9.5.3); the default 200 mm suits a Ø16 vertical with Ø8 links. Vertical bars add a lap of 40 db in compression per §8.7 (60 db selectable for tension or seismic splices) wherever the height exceeds a 6 m stock length, plus 0.5 m for starter projection and bends.
Formulas
Square: V = a² × H. Rectangular: V = b × h × H. Circular: V = π/4 × D² × H. Concrete self-weight at 2,400 kg/m³. Link perimeter = 2 × ((b − 2·cover) + (h − 2·cover)) + hook allowance with 30 mm cover; circular links use π × (D − 2·cover). Weights are tonnes once self-weight exceeds 1,000 kg.
FAQ
What is the minimum column size? EC2 has no absolute minimum, but 200 mm is the practical floor for cast-in-situ columns and 250 mm in seismic zones so the cage, cover, and aggregate fit. How many bags per column? A 300×300×3 m column is about 0.27 m³ — roughly 11–12 bags of 50 kg or 23 bags of 25 kg mix; beyond three or four columns a small ready-mix load is usually cheaper. 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 — the shape tabs compare them directly. Connecting kerb-and-gutter or stair flights belong on their own calculators.
On pour day
Three column-specific traps. Short-load surcharge — six 300×300×3 m columns are ~1.6 m³ which, in most EU markets, attracts a small-load fee (typically €40–90) on top of base ready-mix at €110–160/m³ for C30/37; bagged 50 kg mix at ~€7.50/bag is competitive up to about 1 m³. Starter dowels and laps — vertical bars need a 40 db compression splice (60 db for tension or seismic Class B per EC2 §8.7) wherever a 6 m stock bar runs out; this calc already adds one lap above 6 m of height plus a 0.5 m starter/bend allowance. Link spacing and concrete cover — keep ties at the lesser of 20 db·vert, the smallest column dimension and 400 mm (§9.5.3), and use 30 mm clear cover for XC1/XC2 (rise to 40 mm for XC4 or marine). For tall lifts past 3 m, allow for a boom pump (€500–900 minimum in 2025 EU).
