Concrete Column Calculator
This professional-grade concrete column calculator helps builders, engineers, and DIYers compute the exact volume of concrete required for circular or rectangular columns, add a waste allowance, estimate weight, and determine the number of ready-mix bags. Designed for accuracy, accessibility, and fast decision-making on any device.
Calculator
Results
Bags required (rounded up)
40 lb bag (0.30 ft³)
60 lb bag (0.45 ft³)
80 lb bag (0.60 ft³)
20 kg bag (~0.009 m³)
25 kg bag (~0.012 m³)
30 kg bag (~0.014 m³)
Data Source and Methodology
Authoritative reference: American Concrete Institute (ACI), “ACI 211.1-91 (Reapproved 2009): Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete,” Farmington Hills, MI. Typical unit weight of normal-weight concrete is approximately 145–155 lb/ft³ (≈2320–2480 kg/m³). Direct link.
Bag yields are based on manufacturer data (e.g., QUIKRETE Concrete Mix): 40 lb → 0.30 ft³, 60 lb → 0.45 ft³, 80 lb → 0.60 ft³. See QUIKRETE specifications.
All calculations are strictly based on the formulas and data provided by this source.
The Formula Explained
Circular column volume:
V_c = π (D/2)^2 H
Rectangular column volume:
V_r = W · T · H
Total with waste and count:
V_total = n · V · (1 + w/100)
Mass (weight):
m = ρ · V_total
Unit conversions:
1 ft = 0.3048 m, 1 in = 0.0254 m, 1 yd³ = 0.764554857984 m³, 1 m³ = 35.3146667 ft³
Glossary of Variables
- D: Column diameter
- W: Column width (rectangular)
- T: Column depth/thickness (rectangular)
- H: Column height
- V: Volume of a single column
- n: Number of identical columns
- w: Waste allowance (%)
- V_total: Total concrete volume including waste
- ρ (rho): Concrete density (kg/m³ or lb/ft³)
- m: Mass (kg or lb)
How It Works: A Step-by-Step Example
Scenario: 4 circular columns, diameter 12 in, height 10 ft, waste 7%.
- Convert dimensions: D = 12 in = 1 ft; H = 10 ft.
- Single column volume: V = π (0.5 ft)^2 (10 ft) = π × 0.25 × 10 = 7.85398 ft³ ≈ 0.29126 yd³.
- Total before waste: 4 × 0.29126 = 1.16504 yd³.
- Add waste: V_total = 1.16504 × (1 + 0.07) = 1.2456 yd³.
- 80 lb bags: each yields 0.60 ft³ = 0.02222 yd³ → 1.2456 / 0.02222 = 56.1 → round up = 57 bags.
Using ρ = 2400 kg/m³, V_total = 1.2456 yd³ = 0.952 m³ → mass ≈ 2400 × 0.952 = 2285 kg.
Frequently Asked Questions (FAQ)
Does this calculator include footing or pedestal volumes?
No. It only covers the column itself. Calculate footings separately and add the volumes.
Should I deduct the volume of rebar cages?
Typically unnecessary for small columns. For heavily reinforced columns, deduct the steel volume if precision is critical.
What density should I choose for lightweight or heavyweight concrete?
Lightweight mixes can be 1600–2000 kg/m³; heavyweight mixes exceed 2600 kg/m³. Consult mix design or supplier data.
How much waste should I allow?
Commonly 5–10%. Increase for complex forms, tight rebar, hot/windy conditions, or long pump lines.
Are bag yields the same across brands?
Yields vary slightly by manufacturer and mix. Always verify the product sheet and round up your bag count.
Can I enter dimensions in mixed units (e.g., inches for diameter and feet for height)?
Yes. Change the global length unit to the one you’re entering at that moment; the calculator converts internally.
How does this compare to ready-mix orders?
Ready-mix is typically ordered in cubic yards (US) or cubic meters (SI). This tool outputs both to simplify ordering.