Concrete / Volume Estimator
Estimate the volume of concrete needed for a slab, round slab, or post hole — in cubic yards and cubic meters — plus bags required and an optional cost.
Choose a shape, enter dimensions, and click Estimate.
This is a simple volume estimate. It does not account for reinforcement, irregular subgrade, spillage, or mix design. Always order a little extra and check with your supplier.
How to use
- Choose the shape of your concrete pour — rectangular slab, round slab, or post hole.
- Enter the dimensions for that shape. For a slab, enter length, width, and depth. For a round slab, enter radius and depth. For post holes, enter radius, depth, and quantity.
- Pick your units — feet/inches or meters. When using feet, enter depth in inches and the calculator converts it.
- Optionally choose a bag size and price per bag to estimate how many bags you need and what they will cost.
- Click Estimate concrete to see the volume and bag breakdown.
When people use this
- Pouring a concrete patio, shed base, or garage floor
- Estimating concrete for fence post holes or deck footings
- Planning a round concrete pad for a hot tub, fire pit, or playground
- Figuring out whether to order ready-mix or mix on-site from bags
- Budgeting for a small concrete pour before getting quotes
Examples
Slab: 10 ft × 8 ft × 4 in deep. Volume ≈ 0.99 cubic yards (≈ 0.76 m³). At 80 lb bags, roughly 56 bags.
Round slab: radius 5 ft, 4 in deep. Volume ≈ 0.48 cubic yards (≈ 0.37 m³). At 80 lb bags, roughly 27 bags.
Post holes: 10 holes, 10 in diameter (0.42 ft radius), 2 ft deep each. Volume ≈ 1.15 cubic yards (≈ 0.88 m³). At 80 lb bags, roughly 65 bags.
Frequently asked questions
How accurate is this estimate?It gives a reasonable starting point based on simple geometry. Real pours vary due to subgrade unevenness, spillage, formwork, and reinforcement, so most people order a little extra.
Should I order ready-mix or bags?For small jobs, bags are convenient. For larger pours, ready-mix truck delivery is usually cheaper and faster — but you need to order the whole amount at once and have a place for the truck to access the site.
What depth should my slab be?That depends on what you are building. A shed base or walkway might be 4 in; a driveway or heavy-use slab often needs 5–6 in or more. Check local recommendations for your project.
How do I convert inches to feet for depth?Divide inches by 12. For example, 4 in = 4/12 = 0.33 ft. The calculator does this when you choose feet units.
How many bags are in a cubic yard?It depends on bag size. As a rough guide: about 45 bags of 80 lb concrete make a cubic yard; about 60 bags of 60 lb. Check the yield printed on your bag.
Does this include reinforcement or gravel base?No — this is concrete volume only. A gravel base, rebar, mesh, and other materials are separate.