The honest answer: it depends on what you're pouring, how thick, and whether the ground is level. But you can get a usable number in 30 seconds. Here's how the math actually works, plus the rules of thumb pros use to avoid running short or wasting half a yard.

The basic formula

Concrete is sold by the cubic yard. To find how many cubic yards you need, multiply length × width × depth in feet, then divide by 27 (since one cubic yard = 27 cubic feet).

Example: a 10 ft × 10 ft patio at 4 inches thick = 10 × 10 × 0.333 = 33.3 cubic feet ÷ 27 = 1.23 cubic yards. Add 10% for spillage and over-dig and you're ordering 1.4 yards. Most ready-mix plants have a 1-yard minimum, so you're fine.

Use the concrete calculatorif you don't want to do this by hand — it gives you cubic yards plus the equivalent in 60lb and 80lb bags.

Bags vs ready-mix: where the line is

Bagged concrete makes sense for small jobs. Above about half a cubic yard, ready-mix delivery wins on price, time, and consistency.

A 60lb bag yields 0.45 ft³. An 80lb bagyields 0.60 ft³. So a yard of concrete is roughly 60 bags of 60lb or 45 bags of 80lb. At Home Depot prices in 2026, that's $250–350 in bags vs $150–200 from a ready-mix plant — for the same amount.

The other factor: mixing 45 bags by hand takes hours and gives you inconsistent slump (water content varies bag to bag, your fatigue affects mix quality). Ready-mix shows up in a truck, ready to pour.

Rough decision tree:

  • Under 0.25 yd³ (≈ a 4×4 ft pad): bags, easy
  • 0.25–0.5 yd³ (≈ shed pad, small walkway): bags if you have a mixer, otherwise call ready-mix
  • 0.5+ yd³: ready-mix, every time

How thick should the slab be?

Slab thickness depends on what's rolling on it:

  • 4 inches — patios, walkways, shed floors, garden borders. Standard residential thickness.
  • 4–6 inches — driveways, with rebar or wire mesh. 6 inches if the soil is soft or you park heavy vehicles.
  • 6 inches — garage floors, RV pads, anywhere a heavy truck will park.
  • 8–12 inches — footings under load-bearing walls, pier footings. Always check local code; some jurisdictions require deeper.

The thicker you go, the more concrete you need (linearly), but also the more reinforcement matters. A 4-inch slab can usually skip rebar with proper subgrade prep; a 6-inch slab almost always needs it.

The waste factor everyone forgets

Add 10% to whatever the calculator says. Reasons:

  • Subgrade is never perfectly flat — low spots eat extra concrete
  • Forms can deflect outward as the wet concrete pushes against them
  • Some concrete sticks to the chute, the wheelbarrow, your boots
  • You always over-dig the form perimeter slightly

Coming up half a yard short with the truck pulling away is way worse than having a quarter-yard of leftover concrete you dump into a quick stepping stone form. Always order the next ¼ yard up.

Common pours and their concrete needs

Quick-reference numbers for typical residential pours at 4 inches thick (add 10% waste before ordering):

  • 4×4 shed pad → 0.20 yd³
  • 10×10 patio → 1.25 yd³
  • 12×24 driveway slab → 3.6 yd³
  • 24×24 garage floor → 7.1 yd³
  • Sidewalk, 3 ft × 50 ft → 1.85 yd³

What ready-mix delivery actually costs

Material is around $150–180 per yard depending on PSI and your region. But there are extra fees that catch first-timers:

  • Short-load fee: $50–150 for orders under 3 yards (the truck holds 10 yd³ — they want you to use more of it)
  • Wait fee: $1–3 per minute past the first 5–7 minutes of pouring. Have your form prep, wheelbarrows, and crew ready before the truck arrives.
  • Pump rental: $400–800 if you can't reach the pour from the chute. Skip if at all possible.
  • Saturday/evening: 10–25% surcharge, depending on the plant

Quick FAQ

How much does 1 yard of concrete cost installed? $150–250 DIY (just material), $400–700 if you hire a contractor for a typical pour (includes prep, forms, finish).

How long does concrete take to cure?Foot traffic in 24 hours, light vehicle in 7 days, full strength in 28 days. Don't let anything sit on it for the first 24h.

Do I need to order steel mesh or rebar? For a 4-inch patio: optional but recommended. For a driveway: yes. For a garage floor: definitely.

Run the numbers: the concrete calculator gives you cubic yards, plus the equivalent in 60lb and 80lb bags so you can compare bagged vs ready-mix at a glance.