Concrete Bag Calculator
Enter slab, footing, or pad dimensions and choose a common thickness. The calculator estimates total concrete volume and how many bags to buy, with Imperial and Metric support.
Last updated: May 2026
Buying and sizing notes
- For larger pours, ready-mix delivery may be more practical than mixing many bags by hand.
Concrete bag estimate tips
Small concrete projects are easy to underbuy because a small thickness change creates a big volume change. Use the diagram and thickness presets first, then adjust bag yield to match the product you are actually buying.
Use real thickness
A slab entered as 4 inches is very different from 3 inches or 5 inches. If the base is uneven, use the average finished thickness plus a little extra allowance.
Check the bag yield
Different bag weights and mixes cover different volumes. Use the cubic-foot yield printed on the bag when possible.
Round up early
For hand-mixed projects, one extra bag is usually cheaper than stopping mid-pour to buy more material.
Use bag size carefully
A 60 lb bag, 80 lb bag, and high-strength mix can all have different yields. The bag count changes when the yield changes.
How to use this estimate
What this includes
- Slab volume from length, width, and thickness
- Waste allowance
- Bag yield / bag size assumptions
- Imperial and metric dimension inputs
What it does not include
- Subgrade preparation
- Reinforcement
- Formwork
- Ready-mix delivery minimums
- Local concrete requirements
Common mistakes
- Entering thickness in feet instead of inches
- Forgetting uneven ground below the slab
- Forgetting to round up bags
- Skipping extra material on small pours
Quick questions
How many 80 lb bags of concrete do I need?
Enter the length, width, and thickness of the slab and set the bag yield to the value shown on the 80 lb bag. The calculator rounds up to full bags and includes the waste allowance you choose.
Should I round up concrete bags?
Yes. Running short on concrete is usually worse than having an extra bag or two, especially on small projects.
What concrete thickness should I use?
A 4 inch slab is a common planning starting point for many patios and walkways. Heavier use, poor base conditions, vehicles, frost, or structural requirements can require a different design.
Does this include waste?
Yes, if you leave a waste allowance entered. The default is a planning buffer, not a guarantee.
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