Published March 7, 2026

How Much Concrete Do I Need? Calculating Yards for Any Project

Ordering the right amount of concrete can save you hundreds of dollars and hours of frustration. Order too little and your ready-mix truck leaves before the pour is finished. Order too much and you are paying for concrete you dump in a wheelbarrow. This guide walks you through the volume formulas for slabs, footings, post holes, and stairs, shows you how to add the right waste factor, and breaks down what ready-mix concrete actually costs in different regions.

The Fundamental Concrete Volume Formula

Every concrete calculation starts with the same basic idea: you are filling a three-dimensional space, and you need to know the volume of that space in cubic yards. Ready-mix concrete is sold by the cubic yard in the United States, and one cubic yard equals 27 cubic feet.

Volume (cubic yards) = Length (ft) × Width (ft) × Depth (ft) ÷ 27

The key is getting all three dimensions into feet before multiplying. Depth is almost always given in inches, so divide inches by 12 first. A 4-inch slab is 0.333 feet deep. A 6-inch slab is 0.5 feet deep.

Quick Example

A 20-foot by 10-foot patio that is 4 inches thick:

  1. Convert depth: 4 inches ÷ 12 = 0.333 feet
  2. Calculate volume: 20 × 10 × 0.333 = 66.67 cubic feet
  3. Convert to cubic yards: 66.67 ÷ 27 = 2.47 cubic yards
  4. Add 10% waste factor: 2.47 × 1.10 = 2.72 cubic yards
  5. Round up to order: 3 cubic yards

Calculating Concrete for Slabs

Slabs are the most common concrete project for homeowners. This includes patios, driveways, garage floors, sidewalks, and shed pads. Slabs are rectangular or can be broken into rectangular sections.

Recommended Slab Thicknesses

  • Walkways and garden paths: 4 inches
  • Patios: 4 inches
  • Residential driveways (cars): 4–5 inches
  • Driveways (trucks, RVs): 5–6 inches
  • Garage floors: 4–6 inches (check local code)
  • Shed pads: 4 inches
  • Basketball courts: 4 inches

Example: Driveway Calculation

A typical two-car driveway is 20 feet wide and 40 feet long, poured 5 inches thick:

  1. Depth in feet: 5 ÷ 12 = 0.4167 feet
  2. Volume: 20 × 40 × 0.4167 = 333.33 cubic feet
  3. Cubic yards: 333.33 ÷ 27 = 12.35 cubic yards
  4. With 10% waste: 12.35 × 1.10 = 13.58 cubic yards
  5. Order: 14 cubic yards

Calculating Concrete for Footings

Footings support walls, decks, and other structures. They are typically rectangular trenches dug below the frost line. Footing dimensions are usually specified by building code based on the load they must carry.

Common residential footing sizes are 12 inches wide by 8 inches deep for single-story structures, and 16–24 inches wide by 8–12 inches deep for two-story buildings. The calculation is the same slab formula, but applied to the trench dimensions.

Example: Garage Footing

A 24 × 24-foot detached garage has a continuous footing 16 inches wide and 8 inches deep around the perimeter:

  1. Perimeter: (24 + 24) × 2 = 96 linear feet
  2. Width in feet: 16 ÷ 12 = 1.333 feet
  3. Depth in feet: 8 ÷ 12 = 0.667 feet
  4. Volume: 96 × 1.333 × 0.667 = 85.33 cubic feet
  5. Cubic yards: 85.33 ÷ 27 = 3.16 cubic yards
  6. With 10% waste: 3.16 × 1.10 = 3.48 cubic yards — order 3.5 or 4

Calculating Concrete for Sonotubes and Post Holes

Deck posts, fence posts, and column piers use cylindrical forms called sonotubes. The formula for a cylinder is different from a rectangle:

Volume = π × r² × Height

Where r is the radius (half the diameter) and all measurements are in feet. Then divide by 27 for cubic yards.

Example: Deck Pier Calculation

You are pouring 12 concrete piers using 12-inch diameter sonotubes, each 48 inches deep:

  1. Radius: 12 inches ÷ 2 = 6 inches = 0.5 feet
  2. Depth: 48 inches = 4 feet
  3. Volume per tube: 3.14159 × 0.5² × 4 = 3.14159 × 0.25 × 4 = 3.14 cubic feet
  4. Total for 12 tubes: 3.14 × 12 = 37.70 cubic feet
  5. Cubic yards: 37.70 ÷ 27 = 1.40 cubic yards
  6. With 10% waste: 1.40 × 1.10 = 1.54 cubic yards — order 1.75 or 2

Sonotubes: Volume Per Tube

For quick reference, here is the volume per foot of depth for common sonotube sizes:

  • 8-inch diameter: 0.35 cubic feet per foot of depth
  • 10-inch diameter: 0.55 cubic feet per foot of depth
  • 12-inch diameter: 0.79 cubic feet per foot of depth
  • 16-inch diameter: 1.40 cubic feet per foot of depth
  • 18-inch diameter: 1.77 cubic feet per foot of depth

Calculating Concrete for Steps and Stairs

Concrete stairs are more complex because each step is a smaller volume stacked on a larger base. The easiest approach is to calculate each step individually and add them together.

A standard exterior step is 7.5 inches tall (rise) and 11 inches deep (run), with the width matching the stairway width. Each step sits on top of the concrete below it, forming a layered structure.

Example: Front Porch Steps

Three steps, each 4 feet wide, with a 7.5-inch rise and 11-inch run:

  1. Bottom step (full platform): 4 ft wide × 2.75 ft deep (33 inches total run) × 0.625 ft tall (7.5 in) = 6.88 cu ft
  2. Middle step: 4 ft × 1.833 ft (22 in remaining) × 0.625 ft = 4.58 cu ft
  3. Top step: 4 ft × 0.917 ft (11 in) × 0.625 ft = 2.29 cu ft
  4. Total volume: 6.88 + 4.58 + 2.29 = 13.75 cu ft
  5. Cubic yards: 13.75 ÷ 27 = 0.51 cubic yards
  6. With 10% waste: 0.56 cubic yards

For stairs, a 10–15% waste factor is appropriate because the forms are more complex and some waste is unavoidable.

The Waste Factor: How Much Extra to Order

Always order more concrete than your exact calculation. Concrete is not poured into perfectly measured molds — the ground is uneven, forms can bow slightly, and some material is always lost during placement.

  • Slabs on well-prepared, level ground: add 5–10%
  • Footings in hand-dug trenches: add 10–15% (trenches are rarely perfectly uniform)
  • Sonotubes: add 10%
  • Steps and complex forms: add 10–15%
  • Slabs over gravel or uneven subgrade: add 10–15%

Running short mid-pour is far worse than having a little left over. You can always use extra concrete to fill sonotubes, make stepping stones, or build small pads. But a cold joint from a second delivery compromises the slab's strength.

Ready-Mix vs. Bagged Concrete

For small projects under about 1 cubic yard, mixing bags yourself can be practical. Beyond that, ready-mix delivery is almost always better.

Bagged Concrete

  • An 80-pound bag yields about 0.6 cubic feet of mixed concrete
  • You need 45 bags per cubic yard
  • Cost: roughly $5–7 per 80-lb bag, so $225–$315 per cubic yard in materials alone
  • Mixing 45 bags takes 3–5 hours of heavy labor
  • Best for: post holes, small pad repairs, setting mailbox posts

Ready-Mix Delivery

  • Cost: $130–$170 per cubic yard for the concrete itself
  • Delivery fee: $50–$100 per trip (often waived above a minimum order)
  • Short-load fee: $40–$80 per yard below the minimum (usually 3–5 yards minimum)
  • Overtime charge: $2–$5 per minute if the truck stays beyond 60–90 minutes
  • Best for: any project over 1 cubic yard

Even with the short-load fee, ready-mix for 2 cubic yards often costs less than buying and mixing 90 bags yourself, and it takes 30 minutes instead of a full day of back-breaking work.

Concrete Cost Estimates by Region

Concrete prices vary significantly by location, time of year, and demand. Here are approximate 2025–2026 ranges for ready-mix concrete in the United States:

  • Northeast (NY, NJ, CT, MA): $150–$190 per cubic yard
  • Southeast (FL, GA, NC, TX): $120–$155 per cubic yard
  • Midwest (IL, OH, MI, MN): $130–$160 per cubic yard
  • West Coast (CA, WA, OR): $155–$200 per cubic yard
  • Mountain West (CO, UT, AZ): $135–$170 per cubic yard

These are material-only prices. Total installed cost including labor, grading, forms, rebar, and finishing ranges from $8–$18 per square foot for a standard 4-inch slab.

Reinforcement: Rebar and Wire Mesh

Concrete is strong in compression but weak in tension. Reinforcement helps prevent cracking from shrinkage, temperature changes, and ground movement.

  • Welded wire mesh (WWM): a grid of steel wires used in slabs. Common size is 6x6 W1.4/W1.4 (6-inch grid, 10-gauge wire). Costs $0.15–$0.25 per square foot. Good for patios, walkways, and light-duty slabs.
  • Rebar (#3 and #4): steel bars placed in a grid pattern for driveways, garage floors, and structural slabs. #4 rebar (1/2 inch) on 18-inch centers is typical. Costs $0.60–$1.00 per linear foot.
  • Fiber mesh: synthetic or steel fibers mixed into the concrete. Reduces shrinkage cracking but does not replace structural rebar. Added at the batch plant for about $8–$12 per cubic yard.

Curing: The Most Overlooked Step

Proper curing is critical to concrete strength and durability. Concrete does not "dry" — it hydrates. The cement particles need water to form the crystite structures that give concrete its strength.

  • Keep it moist: spray with water 2–3 times per day for the first 7 days, or apply a liquid curing compound immediately after finishing
  • Keep it covered: in hot, windy, or dry conditions, cover with wet burlap and plastic sheeting
  • Control temperature: concrete should not freeze for at least 48 hours after placement. In cold weather, use insulating blankets or heated enclosures
  • Avoid surface drying: if the surface dries out while the interior is still wet, it will crack, scale, or become dusty

Concrete reaches about 70% of its design strength at 7 days and 99% at 28 days. You can walk on it after 24–48 hours, drive on it after 7 days, and place heavy loads after 28 days.

Common Mistakes to Avoid

After years of concrete projects, contractors see the same mistakes repeated by DIYers:

  1. Not compacting the subgrade — Pour on loose fill dirt and your slab will crack. Compact the base with a plate compactor or hand tamper.
  2. Skipping the gravel base — A 4-inch layer of compacted gravel provides drainage and prevents frost heave. Without it, water accumulates under the slab and causes movement.
  3. Forgetting control joints — Concrete will crack. Control joints (scored lines) tell it where to crack. Space them every 8–12 feet for a 4-inch slab, and the rule of thumb is 2–3 times the slab thickness in feet.
  4. Adding too much water — Extra water makes concrete easier to work but dramatically weakens it. A 4,000-PSI mix can drop to 2,000 PSI if you add extra water. Let the batch plant set the slump.
  5. Working the surface too soon — Finishing before the bleed water evaporates traps water under the surface, causing scaling and delamination. Wait until the sheen disappears before troweling.

Frequently Asked Questions

How many bags of concrete are in a cubic yard?

For standard 80-pound bags of pre-mixed concrete, you need approximately 45 bags to make one cubic yard. For 60-pound bags, you need about 60 bags per cubic yard, and for 40-pound bags, about 90 bags. Each 80-pound bag yields roughly 0.6 cubic feet of mixed concrete, and there are 27 cubic feet in a cubic yard (27 / 0.6 = 45). For projects requiring more than about 1 cubic yard, ordering ready-mix delivery is usually cheaper and much faster than mixing bags by hand.

How much does a cubic yard of concrete weigh?

A cubic yard of standard concrete weighs approximately 4,050 pounds, or about 2 tons. This can vary slightly based on the mix design — lightweight concrete mixes weigh around 3,000 pounds per yard, while heavy mixes with dense aggregates can weigh over 4,500 pounds. Wet (freshly poured) concrete weighs slightly more than cured concrete due to the water content. Knowing the weight matters for delivery planning, structural load calculations, and determining whether your subgrade can support the concrete.

How thick should a concrete slab be?

The required thickness depends on the slab's purpose. Standard residential patios and walkways should be 4 inches thick. Residential driveways need at least 4 inches, with 5–6 inches recommended for heavy vehicles like trucks or RVs. Garage floors should be 4–6 inches thick. Commercial or industrial slabs typically require 6–8 inches or more. Building code in most areas requires a minimum of 3.5 inches for any structural slab. Thicker slabs cost more but provide significantly more strength and crack resistance.

Can you pour concrete in the rain?

You should not pour concrete during heavy rain or if rain is expected within 2–4 hours of placing. Rainwater dilutes the surface paste, weakens the top layer, causes scaling, and creates a dusty or flaky finish. Light mist or drizzle after the concrete has been placed and bull-floated is less damaging, but you should still cover it with plastic sheeting. If rain begins during a pour, cover the concrete immediately with plastic, do not work rainwater into the surface, and resume finishing only after the water evaporates.

How long does concrete take to cure?

Concrete reaches about 70% of its full strength in 7 days and 99% of its strength in 28 days under normal conditions (around 70°F and adequate moisture). You can walk on concrete after 24–48 hours, drive on a driveway after 7 days, and place heavy loads after 28 days. During the critical first 7 days, keep the surface moist by spraying with water, applying a curing compound, or covering with wet burlap and plastic sheeting. Hot weather, low humidity, and wind accelerate surface drying and can cause cracking.