About the concrete bag calculator
Bagged concrete is sold by dry weight, but what you need to know is how much volume each bag produces once mixed. That figure — the yield — is printed on most bags. This calculator lets you enter it directly, so the result matches the exact product you are buying.
If you leave the yield blank, the calculator uses a typical estimate (an 80 lb bag ≈ 0.60 ft³) and says so in the results. It also shows how many bags you would need at the other common sizes, which helps when deciding between lighter bags that are easier to carry and heavier bags that mean fewer trips.
How to use it
- Enter the job as length × width × depth, or type in a volume you already know.
- Enter the bag size you plan to buy.
- Copy the yield from the bag (for example "yields 0.60 cu ft") into the yield field for the most accurate count.
- Add your price per bag to see the cost and the total weight you will be handling.
Formula
Volume
V = length × width × depth (or entered directly)With waste
V_order = V × (1 + waste % ÷ 100)Bags
bags = ⌈ V_order ÷ yield per bag ⌉Typical metric yield estimate
yield ≈ bag mass (kg) × 0.000468 m³/kg (≈ 9.4 L for 20 kg)- The metric estimate is derived from the common US figure of 0.60 ft³ per 80 lb (36.3 kg) and is only a fallback. Products sold in the UK, Canada and Australia list their own yields.
Worked example: A 6 ft × 4 ft pad, 4 in deep
- Volume = 6 × 4 × (4 ÷ 12) = 8 ft³
- With 10 % waste = 8.8 ft³
- 80 lb bags at 0.60 ft³: 8.8 ÷ 0.60 = 14.7 → 15 bags
- Compare: 60 lb → 20 bags, 50 lb → 24 bags, 40 lb → 30 bags
Result: Buy 15 × 80 lb bags (about 1,200 lb to carry).
Assumptions and limitations
- Yields vary by product type (standard, high-strength, fast-setting) and manufacturer; always prefer the printed figure.
- Comparison rows for other bag sizes use typical estimated yields.
- Bags are rounded up individually; buying one spare bag is often worthwhile for small jobs.
Frequently asked questions
How much does an 80 lb bag of concrete make?
Many US 80 lb bags of standard mix state a yield of about 0.60 ft³ (≈17 L). Check your bag — specialist mixes can differ.
How many bags for a fence post?
Calculate the hole volume (use the round column option in the Concrete Calculator), subtract the post volume if you wish, then divide by the bag yield. Fast-setting post mixes often state their own yield per hole size.
Are 60 lb bags better than 80 lb bags?
They produce less concrete each, so you need more of them, but they are easier to lift. The total weight carried is similar; choose what you can handle safely.
Why does the calculator say the yield is estimated?
Because you left the yield field blank. Enter the yield printed on your product and the note disappears.
Sources and further reading
- QUIKRETE — Product calculators (bag-count examples)
- Sakrete — Project calculators
- NIST — Unit conversion (SI and US customary units)
Results are estimates for planning purposes. See our disclaimer for details.