Concrete Footing Calculator
The Concrete Footing Calculator estimates the volume and weight of concrete needed for continuous strip footings, spread footings, and isolated pad footings. Convert length, width, and depth to cubic yards, 60-pound and 80-pound bag counts, weight, and ready-mix cost in seconds.
Continuous strip footings: typically 16–24 in. wide.
Frost-line dependent — most US codes require 8–12 in.
Definition
What is a concrete footing?
A concrete footing is a structural pad poured below the frost line that spreads building load to the soil. Footings prevent foundation settlement, transfer compressive load through reinforced concrete, and anchor walls or columns above. Three footing types cover most residential pours:
- Continuous (strip) footing — a long rectangular trench supporting a foundation wall. Common width: 16–24 in (40.6–61 cm).
- Spread footing — a wider square or rectangular pad under a column or post. Sized for the load above and the soil bearing capacity.
- Isolated pad footing — an individual pad for an interior column or pier, typically 24–36 in (61–91 cm) square.
The math
How to calculate footing concrete
Footing volume equals length × width × depth, in consistent units. Convert width and depth from inches to feet, then multiply by total length to get cubic feet. Divide cubic feet by 27 to convert to cubic yards.
Multiply by (1 + waste%). 10% is the residential default.
Worked example: a 40 ft footing, 16 in wide and 8 in deep equals 40 × (16 ÷ 12) × (8 ÷ 12) = 35.55 ft³ ÷ 27 = 1.32 cubic yards. Add 10% waste — order ~1.45 yd³.
Interactive diagram
See the footing in cross-section
Drag the sliders to resize the footing width and depth. Click a climate region to move the frost line indicator. The footing must extend below the frost line for the structure to resist heave.
Cold climate · frost line at 36 in (91 cm). Footing depth must extend below the frost line — most US codes require a 12″ minimum.
Code requirements
Footing depth and the frost line
Footing depth must extend below the local frost line to prevent frost heave. Frost penetration varies by US climate zone — verify exact requirements with your local building department before pouring.
| Region | Typical frost depth | Minimum footing depth |
|---|---|---|
| Florida, Texas, Arizona | 0–6 in (0–15 cm) | 12 in (30 cm) |
| California, Georgia, Tennessee | 6–12 in (15–30 cm) | 12–18 in (30–46 cm) |
| Pennsylvania, Ohio, Missouri | 30–36 in (76–91 cm) | 36 in (91 cm) |
| Minnesota, North Dakota, Maine | 42–60 in (107–152 cm) | 48–60 in (122–152 cm) |
Sizing
Footing width by wall thickness
A common rule sizes footing width at 2× the wall thickness it supports, with a 16 inch (40.6 cm) minimum for residential foundations. Soil bearing capacity (typically 1,500–3,000 psf for residential soil) and column load can require wider engineered designs.
| Wall thickness | Minimum footing width | Typical depth |
|---|---|---|
| 8" (20 cm) | 16" (40.6 cm) | 8" (20 cm) |
| 10" (25 cm) | 20" (51 cm) | 10" (25 cm) |
| 12" (30 cm) | 24" (61 cm) | 12" (30 cm) |
Reinforcement
Rebar in concrete footings
Most residential footings include 2–3 horizontal #4 rebar bars (0.5 in / 12.7 mm diameter) running the length of the trench, set 3 inches (7.6 cm) above the bottom on chairs or dobies. Wider footings add transverse pieces every 24 inches. Heavy commercial footings use larger rebar (#5 or #6) at tighter spacing, and sometimes a second mat near the top.
Footing Calculator FAQs
Answers to the most common questions about sizing, pouring, and reinforcing concrete footings.
More calculators
Tools for Every Kind of Pour
Slabs are just the start. Run these calculators for square footings, walls, holes, round footings, columns, circular slabs, tubes, curb and gutter barriers, and stairs — plus pre-mix bag counts, total cost, and concrete weight.
By shape
Round Column Calculator
Round concrete column / pillar calculator — volume from diameter and height for any number of columns.
Open calculatorConcrete Wall Calculator
SoonSolid concrete wall calculator — yards and bags from length, height, and thickness.
Round Slab Calculator
SoonCircular concrete slab calculator from diameter and thickness.
Concrete Stairs Calculator
SoonVolume for cast-in-place concrete stairs by tread, rise, and width.
Sonotube Calculator
SoonConcrete needed to fill cylindrical sonotubes.
Curb & Gutter Calculator
SoonConcrete for poured curbs and gutters.
By project
Post Hole Calculator
SoonConcrete needed per fence post or deck post hole.
Driveway Concrete Calculator
SoonConcrete for residential and heavy-duty driveways with thickness guidance.
Patio Concrete Calculator
SoonConcrete for patios — bag and ready-mix options with cost estimate.
Sidewalk Concrete Calculator
SoonSidewalk concrete by length, width, and thickness.
Foundation Calculator
SoonConcrete for residential foundations — slab + footings.
Garage Floor Calculator
SoonConcrete for garage slab including thickness guidance for vehicle weight.
Shed Foundation Calculator
SoonConcrete pad for sheds and outbuildings.
By output
Concrete Bag Calculator
How many 40, 50, 60, or 80 lb concrete bags do you need? Side-by-side bag counts and total weight for any volume.
Open calculatorCubic Yard Calculator
Convert length, width, and depth to cubic yards of concrete with industry-standard 10% waste factor included.
Open calculatorConcrete Cost Calculator
Estimate ready-mix delivered cost or bagged DIY cost — includes typical short-load fee for orders under 3 yards.
Open calculatorConcrete Weight Calculator
SoonConcrete weight in pounds and tons from cubic yards or cubic feet.
Concrete Mix Ratio Calculator
SoonCement, sand, and aggregate quantities for common DIY mix ratios (1:2:3, 1:2:4).
Related
Rebar Calculator
SoonRebar quantity, total linear feet, and grid spacing for slabs.
Gravel Base Calculator
SoonGravel base needed beneath a concrete slab or footing.
Concrete Curing Time Calculator
SoonCure time to reach foot, vehicle, and full design strength.