Concrete bags calculator for small pours and DIY projects.
Enter project dimensions or a known concrete volume, compare standard bag sizes, and estimate total lifting weight and material cost.
Typical 80 lb yield
0.60 ft³
40 lb
0.30 ft³
60 lb
0.45 ft³
80 lb
0.60 ft³
Calculator
How many concrete bags do you need?
Your bag estimate will appear here
Calculate to compare every common bag size and estimate the preferred option.
Bag yield guide
How bag quantity is calculated
The calculator converts your project to cubic volume, adds the selected waste allowance, divides by typical bag yield, and rounds upward. Product formulations vary, so confirm the yield printed on the bag you will buy.
40 lb bag
Typical yield
0.30 ft³
60 lb bag
Typical yield
0.45 ft³
80 lb bag
Typical yield
0.60 ft³
Formula
Bags needed = round up ((project volume × (1 + waste %)) ÷ bag yield)
Related calculator
Planning a full slab?
Use the main concrete slab calculator for bag quantities, ready-mix delivery loads, cubic yards and supplier pricing in one estimate.
Open slab calculatorFAQ
Concrete bag questions
How many bags of concrete do I need?+
Divide the waste-adjusted project volume by the stated bag yield, then round up. This calculator performs the conversions and compares standard sizes.
How much does an 80 lb bag yield?+
A typical 80 lb bag yields about 0.60 cubic feet. Mix and product specifications differ, so always check the package.
How much waste should I add?+
Five to ten percent is common for small pours. Irregular holes, uneven bases, spillage, and uncertain measurements may justify more.
When is ready-mix better than bags?+
Once a job requires roughly 50 or more bags, ready-mix can become easier and sometimes less expensive. Compare delivery minimums, access, timing, labor and local prices.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs, coverage values or planning allowances.
Project guide
Use this calculator with confidence
Last reviewed: July 19, 2026
This calculator converts a small concrete placement into rounded bag counts for common package sizes. It is most useful for post holes, steps, repairs and small slabs where mixing bags may be practical. The calculation uses entered dimensions and approximate yield per bag; because yield varies by product, moisture and mixing method, the package data sheet is always the final purchasing reference.
How to use it
- 1Measure the concrete shape and select the closest supported geometry.
- 2Enter the finished concrete dimensions.
- 3Choose a waste allowance for spills and uneven excavation.
- 4Compare bag sizes, then verify the selected product yield on its package.
Worked example
A 4 ft × 4 ft pad at 4 in. thick contains about 5.33 ft³. With 10% extra, the order volume is about 5.87 ft³. At an approximate 0.60 ft³ per 80 lb bag, round up to 10 bags.
What the defaults mean
Bag yields
Planning values for comparison; manufacturer data overrides them.
10% extra
Useful for small placements where spills and irregular bases are common.
Whole bags
Purchasing quantities are always rounded upward.
| Bag size | Typical planning yield | Verify before buying |
|---|---|---|
| 40 lb | about 0.30 ft³ | package data sheet |
| 60 lb | about 0.45 ft³ | package data sheet |
| 80 lb | about 0.60 ft³ | package data sheet |
Common measurement mistakes
- Using hole depth that includes gravel below the concrete.
- Assuming all bag brands yield the same volume.
- Rounding down because the decimal looks small.
- Ignoring mixing time, water access and labor for large bag counts.
Limits and safety
- Approximate yields are not product specifications.
- Does not evaluate whether ready-mix delivery is more practical.
- Concrete strength, water ratio and placement method are outside the calculation.
Continue the project
calculate ready-mix slab volume — Compare the same placement in cubic yards or metres.
calculate bags for post holes — Use a cylindrical hole model.
estimate concrete for steps — Model repeated stair geometry.
plan mixer batch count — Estimate how many mixer loads the bag order requires.