CrewMeasure field guide
How Much Concrete Do I Need for a Footing?
Ordering ready-mix concrete is expensive to get wrong in either direction — short a load and you're paying for an emergency small batch; order too much and you're paying to dispose of leftover mix. Here's the math.
Step 1: Convert Everything to Feet
Concrete volume calculations need consistent units. Convert all dimensions — length, width, depth — to feet before calculating. A 12" wide footing is 1 ft; an 8" deep footing is 0.667 ft.
Step 2: Rectangular Footing/Slab Formula
`` Cubic feet = Length (ft) × Width (ft) × Depth (ft) Cubic yards = Cubic feet ÷ 27 ``
Example: A footing 40 ft long, 1.5 ft wide, 0.67 ft deep: 40 × 1.5 × 0.67 = 40.2 cubic feet 40.2 ÷ 27 = 1.49 cubic yards
Step 3: Round Footing/Pier Formula
`` Cubic feet = π × radius² × depth Cubic yards = Cubic feet ÷ 27 ``
Example: A round pier 1 ft diameter (0.5 ft radius), 3 ft deep: 3.14159 × 0.5² × 3 = 2.36 cubic feet 2.36 ÷ 27 = 0.087 cubic yards
Step 4: Add a Waste Factor
Ground isn't perfectly flat, forms aren't perfectly plumb, and some mix always sticks to the truck chute or wheelbarrow. Standard practice is 5–10% waste factor on any concrete order.
`` Final order = Calculated yards × 1.10 ``
Why Ready-Mix Companies Round Up Anyway
Most ready-mix suppliers have minimum load sizes (often 1 yard minimum, sometimes higher for delivery). If your calculated volume is under the minimum, you'll pay the minimum regardless — worth knowing before you're surprised at checkout.
Skip the Manual Math
Try the free Concrete Calculator → — handles rectangular and round pours, converts to cubic yards automatically, and applies a waste factor.
FAQ
Why do concrete calculators use cubic yards instead of cubic feet? Ready-mix concrete is sold and delivered by the cubic yard — it's the standard unit for ordering, so calculators convert to it for you.
What waste factor should I use for a large slab pour? 5–10% is standard for most footings and slabs. Irregular ground conditions or hand-mixed small batches may warrant a higher factor.
Do I need to account for rebar or forms in the concrete volume? No — rebar volume is negligible and is not subtracted from concrete volume in standard practice. Forms are a separate material line, not part of the concrete calculation itself.
Estimates only. Verify footing depth and width requirements against your local code and soil/frost line requirements before pouring.
Start with the measurement you can defend
Good concrete footing volume starts with measurements you can explain to another person on the job. Write down where each dimension came from, what it includes, and what it excludes. A number copied from a sketch, a listing, or a quick visual estimate can be useful for an early budget, but it is not the same thing as a field measurement. Recheck unusual corners, changes in height, openings, transitions, and areas where the material changes. Those small details are often what turn an otherwise sensible estimate into a second trip to the supplier.
Before you move on, compare the measured result with the scale of the job. If a small room suddenly produces a large order, or a large area produces only a few pieces, pause and find out why. Unit mistakes, inch-to-foot conversions, and omitted openings are easier to fix on paper than after material arrives.
It also helps to separate the calculation from the purchase decision. The calculation answers a quantity question. The purchase decision must account for package sizes, available stock lengths, lead time, delivery limits, damage allowance, and whether you need matching material later. Keep the raw result visible, then document the rounding and waste decision you make for the job. That creates a simple record you can revisit if the number looks wrong after layout begins.
The detail that changes the order
One of the most common mistakes with concrete footing volume is using nominal form dimensions without checking depth changes, bell bottoms, or uneven excavation. The arithmetic may still be correct, but the answer is only as useful as the inputs and assumptions behind it. Slow down long enough to compare the result with how the work will actually be installed. Ask whether the material is cut to a pattern, whether a finished dimension differs from a rough dimension, whether a supplier uses a different unit, and whether one part of the job creates extra waste for another. This is especially important when the layout changes direction, includes openings, or needs a material transition.
Use a second check that does not repeat the same calculation. Sketch the area, count the obvious pieces, compare against a previous similar job, or walk the perimeter with a tape. If both approaches land in the same range, the estimate is usually more reliable. If they do not, do not hide the difference by averaging it. Find the assumption that changed. On a jobsite, that usually costs less time than correcting a short order after crews are already waiting.
Work the job in sequence
Before ordering, make a short handoff list: the measured dimensions, the chosen material, the planned waste allowance, any supplier conversion, and the conditions that still need confirmation. Take photos of odd conditions and keep the product data with the estimate. This protects the person buying material from having to guess what the original number meant. It also makes revisions much easier if the owner changes a layout, a room is remeasured, or a product is unavailable.
For safety-critical, code-regulated, structural, electrical, plumbing, or weather-exposed work, a calculator cannot replace a design review. Verify local frost depth, soil conditions, reinforcement, form dimensions, and the ready-mix producer’s order details. Local jurisdictions may amend model codes, and product manufacturers can require details that a generic formula cannot see. When the result affects a permit, load, connection, circuit, pipe, or life-safety decision, involve the appropriate qualified professional before work begins.
Keep a written assumption list
CrewMeasure is most useful when it gives you a transparent starting point instead of a mystery answer. Enter the job measurements, review the assumptions and warnings, and use the output to plan the next conversation with your supplier, inspector, trade partner, or client. The goal is not to make the judgment disappear. The goal is to reduce repetitive math, make the inputs visible, and leave more attention for the conditions that actually need human judgment.