Concrete Calculator
Cubic yards, tons, and 80 lb bag counts for slabs, pads, and footings — with the pour drawn to scale.
Your estimate
You'll need 1.75 cubic yards of concrete — about 74 80 lb bags, roughly $289.
120 sq ft at 4 in thick · 3.31 tons · 44.01 cu ft
Slab size
Concrete details
Patios 4 in · driveways 5–6 in · footings 8–12 in
Subtract cutouts & posts
No openings yet. Add each door or window and its area comes out of the total.
Waste & cost
10% is standard
Your slab drawn to scale at the thickness you selected.
The breakdown
- Cubic yards to order
- 1.75 cu yd
- 80 lb bags
- 74 bags
- 60 lb bags
- 98 bags
- Weight
- 3.31 tons
- Total slab area
- 120 sq ft
- Areas subtracted
- −0 sq ft
- Net area to pour
- 120 sq ft
- Thickness
- 4 in
- Raw volume
- 1.481 cu yd
- Waste overage (10%)
- 0.15 cu yd
- Total volume
- 44.01 cu ft
- Ready-mix cost
- $289
- Bagged costOver a yard — ready-mix is usually cheaper and faster
- $481
Where to buy
Hand-picked search links for the materials on your list. As an Amazon Associate, ProjectMath earns from qualifying purchases.
Prices and availability are set by the retailer and change often. Always confirm the exact product size matches what this calculator assumed.
How this is calculated
Concrete is ordered by volume, so thickness drives everything. Every unit — yards, tons, bags — comes out of the same cubic-foot figure.
- cubic feet = length × width × (thickness in inches ÷ 12)
- cubic yards = cubic feet ÷ 27
- tons ≈ cubic yards × 2.03 (standard mix, ~4,050 lb per yard)
- 80 lb bags = ceil(cubic feet ÷ 0.60) · 60 lb bags = ceil(cubic feet ÷ 0.45)
Ready-mix is usually ordered in quarter-yard increments with a minimum load. Under about a yard, bags win; over it, a truck almost always does.
- 1Measure the surfaceMeasure the width and height (or length) of the area in feet, inches, or meters and enter them in the calculator.
- 2Set the slab thickness4 inches suits a patio or shed pad, 5 to 6 inches a driveway or anything carrying vehicles. Footings are usually 8 to 12 inches deep.
- 3Convert to cubic yardsThe calculator turns length, width, and thickness into cubic feet, then divides by 27 for cubic yards and converts to tons and bag counts.
- 4Add a waste overageKeep 5 to 10% spare. Uneven subgrade quietly eats more concrete than most people expect, and a short pour cannot be fixed later.
- 5Read the shopping listThe calculator rounds up to whole units to buy and multiplies by your price per unit for an estimated total. Copy or print the plan and take it to the store.
Common questions
How much concrete do I need for a slab?
Multiply length by width by thickness in feet, then divide by 27 for cubic yards. A 10 by 10 foot slab at 4 inches thick is about 1.24 cubic yards before waste.
How many 80 lb bags of concrete are in a cubic yard?
About 45. Each 80 lb bag yields roughly 0.60 cubic feet, and a cubic yard is 27 cubic feet. A 60 lb bag yields about 0.45 cubic feet, so it takes around 60 of those.
When should I order ready-mix instead of mixing bags?
Past about one cubic yard — roughly 45 bags — mixing by hand stops making sense on cost, time, and finish quality. Most ready-mix suppliers have a minimum load and a short-load fee below it.
How much does a cubic yard of concrete weigh?
Around 2 tons, or about 4,000 pounds, for standard mix. That is why weight matters for footings and for anything you are hauling yourself.
How thick should a concrete patio be?
4 inches over a compacted base is standard for foot traffic and furniture. Go to 5 or 6 inches where a vehicle will park.