Concrete Calculator
Calculate exactly how much concrete you need for slabs, footings, and columns. Get cubic yards, bag counts, and estimated costs.
How to Calculate Concrete Volume
Calculating concrete volume is straightforward once you understand the basic formula. For rectangular shapes like slabs and footings, multiply length × width × depth. The result in cubic feet is then divided by 27 to convert to cubic yards, which is how ready-mix concrete is sold.
For circular columns, the formula uses π × radius² × height. Enter the diameter and height, and our calculator handles the math automatically.
How Many Bags of Concrete Do I Need?
Pre-mixed concrete bags come in two common sizes. A 60-pound bag yields approximately 0.45 cubic feet of concrete, while an 80-pound bag yields about 0.60 cubic feet. For small projects under 1 cubic yard, bags are often more practical than ordering a ready-mix truck. For larger pours, ready-mix delivery at around $150 per cubic yard is typically more economical.
Concrete Thickness Guide
The right thickness depends on your project. Sidewalks and patios typically need 4 inches, driveways require 4–6 inches depending on vehicle weight, garage floors are usually 4–6 inches, and footings range from 8–12 inches deep depending on load requirements and frost depth.
Tips for Ordering Concrete
- Always order 5–10% extra to account for waste, spillage, and uneven subgrade
- Confirm that your forms are properly braced before the truck arrives
- Have enough labor on hand — concrete waits for no one
- Check weather forecasts — avoid pouring in extreme heat, cold, or rain
Frequently Asked Questions
How much does a cubic yard of concrete weigh?
A cubic yard of concrete weighs approximately 3,900–4,050 pounds (about 2 tons). This is important for planning delivery access and ensuring your subgrade can support the load.
How long does concrete take to cure?
Concrete reaches about 70% of its full strength in 7 days and near-full strength at 28 days. You can typically walk on it after 24–48 hours, but avoid heavy loads for at least a week.
Can I pour concrete in cold weather?
Yes, but temperatures below 40°F require special precautions including heated enclosures, insulating blankets, and possibly accelerating admixtures. Never pour on frozen ground.
What PSI concrete should I use?
For residential slabs and sidewalks, 3,000–3,500 PSI is standard. Driveways should use at least 4,000 PSI. Structural footings and foundations typically require 3,500–4,500 PSI.
How much does ready-mix concrete cost?
Ready-mix concrete typically costs $125–$175 per cubic yard delivered, depending on your region and the mix design. Short-load fees apply for orders under a full truck (usually 8–10 yards).
Should I use bags or ready-mix?
For projects under half a cubic yard, bags are convenient and cost-effective. For anything over 1 cubic yard, ready-mix is faster, provides a more consistent product, and is usually cheaper per yard.
Related Calculators
- Concrete Slab Calculator — slab-specific with rebar and mesh estimates
- Concrete Block Calculator — CMU blocks for walls
- Concrete Driveway Cost Calculator — full cost breakdown by finish type
Estimates only. Consult a licensed professional for your specific project requirements.