Concrete Calculator

How many cubic yards of concrete, or how many 40, 60 and 80 lb bags, you need for a slab, patio, walkway, footing pad or round pier.

Concrete mixer, bag of concrete mix and shovel A portable orange drum concrete mixer on a wheeled frame, an 80 lb paper bag of concrete mix, and a shovel stuck in a small pile of gravel. MIX 140L WATER 3 qt CONCRETE MIX 80 LB 36.3 kg · yields 0.6 cu ft

Prefer your local store? Enter its prices for a cost estimate.

Pour reference

CONCRETE SLAB4 in, wire mesh at mid-depth GRAVEL BASE4 in, compacted SOILfirm and compacted control joint 4 in4 in
Typical section. Driveways and structural slabs: follow local code.

Mix and pour

Water
3 qt / 80 lb bag
Mix time
3–5 min / batch
Working time
60–90 min
Air temperature
50–90 °F
Frost
none for 48 h

Slab

Walks and patios
4 in
Driveways
5–6 in
Gravel base
4 in, compacted
Joint spacing
2–3× thickness, in ft
Joint depth
¼ of slab

Cure

Keep moist
7 days
Foot traffic
24–48 h
Vehicles
7 days
Design strength
28 days

Ordering

80 lb bag
0.6 ft³
1 yd³
45 × 80 lb bags
Weight
≈ 4,000 lb / yd³
Ready-mix
above 1.5 yd³

Safety Wet concrete is caustic. Wear gloves, eye protection and boots; rinse skin contact right away.

Full notes
  • Order 5-10% extra. Subgrade is never perfectly level and forms flex under the weight.
  • Walkways and patios are usually 4 inches thick; driveways and garage slabs are 5-6 inches.
  • Bagged mix is fine for small jobs. Once you need more than about 1.5 cubic yards, ready-mix delivery is usually cheaper and much less work. Most plants have a minimum load, often 1-3 cubic yards, and charge a short-load fee below it.
  • An 80 lb bag yields about 0.6 cubic feet, a 60 lb bag about 0.45, a 40 lb bag about 0.3.
  • Concrete weighs roughly 4,000 lb per cubic yard, so check that your trailer or truck can carry the load.
  • Weather: pour when it is roughly 50-90 °F. Do not pour if frost is expected in the next 24-48 hours; in hot or windy weather mix smaller batches and keep the surface damp.
  • Water: about 3 quarts per 80 lb bag (check your bag). Too much water makes concrete easier to pour but weaker and more prone to cracking. Aim for an oatmeal-like mix that holds its shape.
  • Mixing order in a drum mixer: about two-thirds of the water, then the dry mix, then the rest of the water a little at a time. Mix 3-5 minutes per batch.
  • Working time is about 60-90 minutes after mixing, less in heat. Never add water to a batch that is stiffening.
  • Finishing: screed level, bull-float, wait for the surface water to disappear, then edge, cut control joints (about a quarter of the slab depth) and broom or trowel.
  • Curing: keep the slab damp or covered for at least 7 days. Light foot traffic after 24-48 hours, cars after about 7 days, full strength at about 28 days.
  • Safety: wet concrete is caustic and can burn skin. Wear gloves, eye protection and boots, and rinse any skin contact quickly.

Planning a bigger project?

Gravel CalculatorCubic yards and tons of gravel for a driveway, path, drainage trench or patio base.Topsoil CalculatorCubic yards, tons and bags of topsoil for a new lawn, raised bed or garden, with a bulk-versus-bag cost comparison.Project: Build a PatioAll the calculators for this job in order.

Common sizes

Drag to change the size
12 × 16 ft192 ft²
4 in deep2.61 yd³ · 118 × 80 lb bag6 in deep3.91 yd³ · 176 × 80 lb bag
4 × 8 ft24 × 24 ft

Drag the corner of the shape or the slider. Grid squares are 2 ft. Tap a result to load it into the calculator.