Concrete Footing
Calculate concrete for strip and isolated footings. Enter values for instant results with step-by-step formulas.
Formula
Volume = Length x Width x Depth
Calculate footing volume in cubic feet, then divide by 27 for cubic yards. Add 10% waste factor for safety.
Worked Examples
Example 1: Strip Footing Calculation
Problem:40-foot perimeter wall needs continuous footing, 24\" wide × 12\" deep.
Solution:Length: 40 ft\nWidth: 24\" = 2 ft\nDepth: 12\" = 1 ft\n\nVolume = 40 × 2 × 1 = 80 cubic feet\nCubic yards = 80 ÷ 27 = 2.96 yards\n\nWith 10% waste: 2.96 × 1.10 = 3.26 yards
Result:Order 3.5 cubic yards
Example 2: Isolated Footings
Problem:6 columns need 3×3 ft footings, 18\" deep each.
Solution:Per footing:\n3 × 3 × 1.5 = 13.5 cubic feet\n\nTotal for 6:\n13.5 × 6 = 81 cubic feet\n81 ÷ 27 = 3.0 cubic yards\n\nWith 10% waste: 3.3 yards
Result:Order 3.5 cubic yards for 6 footings
Example 3: Mixed Footing Project
Problem:Calculate concrete for 30 ft strip (2 ft wide) + 4 isolated pads (2.5×2.5 ft), all 12\" deep.
Solution:Strip: 30 × 2 × 1 = 60 cu ft\nPads: 2.5 × 2.5 × 1 = 6.25 cu ft each\nTotal pads: 6.25 × 4 = 25 cu ft\n\nTotal = 60 + 25 = 85 cu ft\n85 ÷ 27 = 3.15 yards\nWith waste: 3.46 yards
Result:Order 3.5-4 cubic yards
Frequently Asked Questions
What is a strip footing?
A strip footing (continuous footing) runs continuously along a wall or foundation line. It distributes the load of a wall over a larger area. Typical dimensions: 2-3 feet wide, 8-18 inches deep. Used for load-bearing walls and foundation perimeters.
What is an isolated footing?
An isolated footing (pad footing) supports a single column or post. It's typically square or rectangular. Size depends on column load and soil bearing capacity. Common sizes range from 2×2 to 6×6 feet with 12-24 inch depth.
How wide should my footing be?
Width depends on wall thickness and soil bearing capacity. Rule of thumb: footing width = 2× wall thickness. For 8\" wall, use 16\" (1.33 ft) minimum footing. Engineer may specify wider for poor soil or heavy loads. Typical range: 16-36 inches wide.
What concrete strength for footings?
Minimum 2,500 PSI for residential footings. 3,000 PSI is common and provides good margin. Commercial or heavy-load footings may require 3,500-4,000 PSI. Check structural drawings or consult engineer for specific requirements.