Concrete Calculator

What Is a Concrete Yard Calculator?

A concrete yard calculator (also called a concrete volume calculator) helps you determine how many cubic yards of concrete you need for your project. Concrete is ordered by the cubic yard in the US — one yard is 3ft × 3ft × 3ft (27 cubic feet). Our calculator converts your slab, footing, column, or wall dimensions into cubic yards automatically, then shows bags needed and estimated cost. Whether you need 2 yards for a patio, 5 yards for a driveway, or 15 yards for a foundation, this tool gives precise yardage with waste factor built in.

Quick Concrete Yardage Reference

Project	Typical Dimensions	Cubic Yards	80-lb Bags
Small patio	10ft × 10ft × 4in	1.2 yd³	~22 bags
Medium patio	12ft × 12ft × 4in	1.8 yd³	~32 bags
1-car driveway	12ft × 20ft × 5in	3.7 yd³	~67 bags
2-car driveway	20ft × 20ft × 5in	6.2 yd³	~112 bags
Walkway	4ft × 30ft × 4in	1.5 yd³	~27 bags
Foundation footing	40ft × 2ft × 12in	3.0 yd³	~54 bags

Pro tip: Ready-mix trucks carry 9-10 yards. For projects under 1 yard use bagged concrete. For 1-3 yards a short-load truck may work. For 3+ yards standard delivery is most economical. Use the calculator above for exact yardage.

How Is Concrete Volume and Yardage Calculated?

In construction and masonry, concrete is quantified in volumetric units—specifically cubic yards (yd³) in the United States and cubic meters (m³) internationally. One cubic yard represents a volume of 3 ft × 3 ft × 3 ft, which equals exactly 27 cubic feet.

1. Rectangular Slab & Trench Footing Volume Equation

Volume (yd³)=

Length (ft) × Width (ft) ×

Thickness (in)12

27 (Cubic Feet per Yard)

2. Pre-Mixed Bag Yield & Column Equations

80-lb & 60-lb Bag Yields

• 80-lb Bags = Volume (ft³) ÷ 0.60 (45 bags / yd³)

• 60-lb Bags = Volume (ft³) ÷ 0.45 (60 bags / yd³)

Round Column / Sonotube

• Radius (ft) = Diameter (in) ÷ 24

• Volume (yd³) = [π × Radius² × Height (ft)] ÷ 27

Step-by-Step Calculation Breakdown

Step 1: Input Dimensions (20 ft Driveway × 10 ft Width × 4 in Depth)

Convert thickness to feet: 4 inches ÷ 12 = 0.3333 ft

Step 2: Calculate Cubic Feet and Cubic Yardage

Volume (ft³) = 20 ft × 10 ft × 0.3333 ft = 66.67 cu ft

Volume (yd³)=

66.67 cu ft27 cu ft/yd³

=2.47 yd³

Step 3: Add 10% Spillage & Subgrade Waste Factor

Total Ordered=2.47 yd³ × 1.10=2.72 yd³ (Order 3.00 Ready-Mix Yards)

Ready-Mix Truck vs. Pre-Mixed Bag Comparison

Pour Option	Project Scale	Bags per Cu Yard	Logistics & Handling Considerations
80-lb Quikrete / Sakrete Bags	< 1.0 cu yd	45 Bags	Best for fence posts, mailbox footings, and minor walkway repairs. Requires drum mixer.
60-lb Pre-Mix Bags	< 0.5 cu yd	60 Bags	Lightweight bag option for tight access spaces where lifting 80 lbs is prohibitive.
Ready-Mix Volumetric Truck	> 1.0 cu yd	Delivered Liquid	Most economical for driveways, patios, and slabs. Consistent hydration and slump.

Recommended Slab Thickness by Application

Application	Minimum Thickness	Recommended	Standard PSI
Walkways & Garden Paths	3.5 inches	4.0 inches	3,000 PSI
Outdoor Patios & Hot Tub Pads	3.5 inches	4.0–5.0 inches	3,500 PSI
Residential Driveways (Passenger Cars)	4.0 inches	5.0 inches	4,000 PSI
Heavy Truck Driveways & RV Pads	5.0 inches	6.0 inches	4,500 PSI

Tips for Accurate Concrete Estimation

Measure accurately: Verify all form dimensions prior to ordering. Subgrade trench excavations are the primary cause of shortfalls.
Account for subgrade variance: Hand-graded dirt and gravel base compaction often vary by ±0.5 inches across a slab span.
Always add a 10% waste buffer: Ready-mix companies charge expensive short-load return trip fees if you run short by even 0.25 yards.

Frequently Asked Questions

How do I calculate how much concrete I need?

Measure the length, width, and depth (thickness) of the area to be filled. Multiply all three dimensions together to get the volume. If using feet and inches, convert the depth to feet first (divide inches by 12). The result is cubic feet. Divide cubic feet by 27 to get cubic yards, which is the standard unit for ordering ready-mix concrete. Our calculator automates all of this, including unit conversions, waste factor, and bag count estimation.

How many bags of concrete do I need?

A standard 80-lb (36 kg) bag of concrete yields approximately 0.6 cubic feet (0.017 cubic meters) of mixed concrete. A 60-lb bag yields about 0.45 cubic feet, and a 40-lb bag yields about 0.3 cubic feet. To find the number of bags needed, divide your total cubic feet by the yield per bag. For example, a 4×8-foot slab that is 4 inches thick requires 10.67 cubic feet ÷ 0.6 = approximately 18 bags (80-lb). Our calculator includes this automatically.

How much does concrete cost?

Ready-mix concrete typically costs $120–$160 per cubic yard for standard mixes, delivered. Prices vary by region, distance from the batch plant, order size, and concrete specification (higher PSI ratings cost more). Bagged concrete (80-lb bags from hardware stores) costs roughly $5–$7 per bag, which translates to $200–$280 per cubic yard — significantly more expensive for large projects. For orders over 3–4 cubic yards, ready-mix delivery is almost always more economical.

Should I order extra concrete for waste?

Yes. Industry standard practice is to order 5–10% more concrete than your calculated volume. This accounts for spillage, uneven subgrade (the ground beneath the concrete), over-excavation, and the concrete that remains in the mixer chute and forms. A 10% overage is standard for most residential projects. For complex forms or sloped subgrade, consider 15%. Running short is far more costly than a small overage — a partial pour that sets before additional concrete arrives creates a cold joint, which is a structural weakness.

What is the difference between cubic yards and cubic feet?

One cubic yard equals 27 cubic feet (3 feet × 3 feet × 3 feet). Cubic yards are the standard ordering unit for ready-mix concrete in the United States and Canada. Cubic feet are useful for smaller calculations and bag estimates. Cubic meters are the standard in most other countries. Our calculator provides results in all three units automatically.

What thickness should I use for a concrete slab?

Standard residential slab thickness depends on the application: driveways require 4–6 inches (6 inches for heavy vehicles), patios and walkways use 4 inches, garage floors need 4–6 inches with thickened edges, and footings typically require 8–12 inches depending on soil conditions and load requirements. Building codes vary by jurisdiction — always verify local requirements before pouring. The American Concrete Institute (ACI) provides detailed specifications in ACI 332R-20 for residential construction.

Project Specifications

Pre-Mixed Bag Estimates