How Much Concrete Do I Need? Complete Guide

Getting your concrete quantity right is one of the most important pre-pour decisions you’ll make. Order too little and you’ll have a cold joint in the middle of your pour. Order too much and you’re paying for concrete that ends up in someone else’s project.

Quick Answer: Volume = Length × Width × Thickness (all in feet) ÷ 27 = cubic yards. Always add 10% for waste. Under 1 cubic yard → bags are usually cheaper. Over 1 cubic yard → order ready-mix.

This guide walks through the complete process of calculating concrete for the most common residential and light commercial applications.

The Core Formula

All concrete calculation starts with one equation:

Volume = Length × Width × Thickness

All three dimensions must be in the same unit before you multiply. Since concrete is ordered in cubic yards in the US, the most convenient approach is to work entirely in feet (converting inches to decimal feet), then divide by 27.

Example: A 12-foot × 20-foot patio slab, 4 inches thick:

• Convert thickness: 4 inches ÷ 12 = 0.333 feet
• Volume in cubic feet: 12 × 20 × 0.333 = 80 cubic feet
• Convert to cubic yards: 80 ÷ 27 = 2.96 cubic yards

You’d order 3.25 cubic yards (adding ~10% for waste).

Use our Concrete Slab Calculator to handle these conversions automatically — it accepts feet and inches separately so you don’t need to do the decimal conversion yourself.

How Much Concrete for a Patio?

A standard backyard patio at 4 inches thick needs approximately:

Patio Size	Cubic Yards
10×10 ft	0.62 yd³
12×16 ft	0.89 yd³
16×20 ft	1.48 yd³
20×30 ft	2.22 yd³

For patios under 1 cubic yard, bag concrete is usually more cost-effective than ordering ready-mix with a minimum delivery charge. One cubic yard is typically the crossover point.

How Much Concrete for a Driveway?

Driveways need more thickness than patios — 4 inches minimum for passenger vehicles, 5–6 inches for pickup trucks and SUVs, and 6 inches if you park heavy equipment.

A typical two-car driveway at 16 ft wide × 40 ft long:

• At 4 inches: 9.88 cubic yards
• At 5 inches: 12.35 cubic yards
• At 6 inches: 14.81 cubic yards

Add 10% waste: order roughly 11, 14, or 16 cubic yards depending on thickness.

Our Concrete Driveway Calculator handles these calculations with options for both standard and heavy-use thickness.

How Much Concrete for Footings?

Footings support the structure above them, so their dimensions are typically specified by an engineer or building code. A common residential footing is 16 inches wide × 8 inches deep for a single-story wall.

Strip footing formula: Length × Width × Depth

For a 60-foot perimeter footing, 16 inches wide × 8 inches deep:

• 60 ft × (16/12) ft × (8/12) ft = 53.33 cubic feet = 1.97 cubic yards

Use the Concrete Footing Calculator to calculate your entire foundation run.

Bags vs. Ready-Mix

Use bags when:

• Total pour is under 1 cubic yard
• You’re doing a repair or small pour
• Ready-mix minimum delivery charges make it uneconomical

Use ready-mix when:

• Total pour exceeds 1 cubic yard
• Consistent mix quality is critical
• You need the pour completed quickly

An 80 lb bag of Quikrete or Sakrete yields 0.60 cubic feet of concrete. To get your bag count from cubic feet: divide total cubic feet by 0.60.

For our example patio at 80 cubic feet: 80 ÷ 0.60 = 134 bags. At that scale, ready-mix is far more practical. Use our Concrete Bags Calculator for small-pour bag counts.

Adding the Waste Factor

Always add extra concrete. Standard practice:

• 5% for a perfectly formed, even-subgrade pour
• 10% for typical residential work
• 15% for slabs on uneven ground or with complex formwork

A short load (running out mid-pour) creates a cold joint — a visible seam where fresh concrete was placed against partially-set concrete. This is a structural weakness and cosmetic problem. It’s far better to have a small amount left over.

Ready-Mix Ordering Tips

1. Order by the yard, not the bag. Give your supplier the cubic yard number and let them convert.
2. Specify your mix design. For residential slabs, 3,000 psi with 3/4” aggregate is standard. For driveways, consider 3,500 psi for better freeze-thaw resistance.
3. Ask about minimum loads. Most suppliers have a 1-yard minimum charge for anything under their minimum (usually 5–7 yards). The “short load” fee can be $50–$100.
4. Confirm slump. A 4–5 inch slump is standard for residential work — workable but not sloppy. High slump adds water and reduces strength.

Frequently Asked Questions

How long does it take to pour concrete? A 10 cubic yard pour takes a typical crew of 3–4 people about 2–3 hours to place and finish. Larger pours should have additional finishers. Ready-mix trucks are typically paid by the hour after the first hour, so having enough help is critical.

Can I pour concrete in cold weather? Concrete can be poured in cold weather with precautions. Protect fresh concrete from freezing for at least 7 days. Use heated water or additives in the mix for temperatures below 40°F. Never pour on frozen ground.

How many square feet does a cubic yard cover? One cubic yard covers:

• 81 sq ft at 4 inches deep
• 54 sq ft at 6 inches deep
• 40.5 sq ft at 8 inches deep

What’s the difference between concrete and cement? Cement is an ingredient in concrete. Concrete = cement + sand + aggregate + water. “I need to order cement” when you mean concrete is a very common mix-up on job sites.

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See also: Concrete Calculation Methodology — the formula derivations, bag yield tables, waste factors, and ACI 318 references behind ConstructCalc concrete calculators.