Concrete Calculator
Free concrete calculator. Enter length, width and depth to get cubic feet, cubic yards and the number of 80 lb or 60 lb concrete bags you need, with waste allowance.
About the Concrete Calculator
Our free concrete calculator tells you exactly how much concrete you need for a slab, footing, sidewalk or post hole. Enter the length, width and depth (thickness) of your pour and the tool instantly returns the volume in cubic feet and cubic yards plus the number of 80 lb and 60 lb premix bags to buy, with an adjustable waste allowance so you never run short mid-pour. You can also set a quantity to estimate several identical pours at once, like fence-post holes or deck piers. Every calculation runs in your browser — no signup, no app, no data sent anywhere — making it perfect for contractors, DIY homeowners and handymen on site.
Features
- Volume in cubic feet and cubic yards from length × width × depth
- Bag count for both 80 lb and 60 lb premix concrete
- Adjustable waste percentage (0–20%) so you order a safe margin
- Quantity field for repeated pours like post holes or piers
- Works for slabs, footings, sidewalks, pads and columns
- 100% client-side and private — instant results, no signup
How to use this tool
The Concrete Calculator works right in your browser — no signup, no installation. Follow these steps:
- Enter the length and width of your pour in feet.
- Enter the depth (thickness) in inches — e.g. 4 for a standard slab.
- Optionally set a quantity for repeated pours and a waste percentage.
- Read off the cubic yards and the number of 80 lb or 60 lb bags to buy.
Frequently asked questions
How do you calculate cubic yards of concrete?
Multiply length × width × depth to get cubic feet, then divide by 27 (since one cubic yard equals 27 cubic feet). Remember to convert the depth from inches to feet first by dividing by 12. This calculator does all of that automatically.
How many square feet does an 80 lb bag of concrete cover?
An 80 lb bag of premix concrete yields about 0.6 cubic feet. At a 4-inch thickness that covers roughly 1.8 square feet, so for a 4-inch slab you need about one 80 lb bag per 1.8 sq ft of surface.
Should I add extra concrete for waste?
Yes. A 5–10% waste allowance covers spillage, uneven subgrade and minor over-pours. This is especially important for bagged concrete, since running out mid-pour causes cold joints. Use the waste slider to add a safety margin.
How many bags are in a cubic yard?
One cubic yard of concrete equals about 45 eighty-pound (80 lb) bags or about 60 sixty-pound (60 lb) bags. The calculator shows both so you can buy whichever size your supplier carries.
Is this concrete calculator free?
Yes, completely free with no signup, no account and no limits. Every calculation runs in your browser, so your project numbers never leave your device.
Using the results
The Concrete Calculator estimates quantities from your measurements and the stated assumptions. Check dimensions, product coverage and project requirements before buying materials.