Concrete Calculator
Calculate concrete volume and bags needed
About the Concrete Calculator
Order too little concrete and a pour stalls; order too much and you have paid for waste. This calculator estimates the volume your project needs and converts it into the number of bags to buy, handling slabs, footings, columns, and tubes.
Contractors and serious DIYers use it before pouring a patio, setting fence posts, or filling form tubes. It works out the volume in cubic yards, adds a waste factor, and tells you how many 40, 60, or 80-pound bags that comes to — with an optional cost estimate so you can budget the trip to the supplier.
How to Use the Concrete Calculator
- Choose your measurement units and the bag size you plan to buy (40, 60, or 80 lb).
- Set a waste factor (5% by default) and, optionally, the price per bag.
- Add each pour, choosing its shape — slab, footing, column, or tube — and entering the dimensions.
- Read the total volume, cubic yards, bags needed for each bag size, and the estimated cost.
Why Use ToolForge’s Concrete Calculator
- It handles four pour types — slabs, footings, columns, and tubes — including the hollow-tube calculation that subtracts the inner void.
- It converts volume into bag counts for all three common bag weights and applies an adjustable waste factor.
- It estimates total cost when you enter a price per bag, so you can budget before buying.
- It computes everything in your browser with no sign-up.
Frequently Asked Questions
How much concrete do I need?
Multiply the length, width, and depth of a slab to get its volume, then convert to cubic yards (dividing cubic feet by 27). Columns and tubes use circular formulas. This calculator does the conversion and adds a waste margin automatically.
Why add a waste factor?
Some concrete is always lost to spillage, uneven subgrade, and over-excavation, so ordering exactly the calculated volume risks coming up short. A 5–10% waste factor — adjustable here — gives a practical buffer.
How many bags of concrete are in a cubic yard?
It depends on bag size: it takes more small bags than large ones to fill the same volume. The calculator uses standard coverage for 40, 60, and 80-pound bags and shows the count for each so you can choose.
When should I order ready-mix instead of bags?
Bags suit small jobs like post holes and small slabs, but for large pours the number of bags becomes impractical and ready-mix delivery is usually cheaper and faster. The bag count here is a good gauge — if it runs into the dozens, price up ready-mix too.
