Concrete Bag Calculator: How Many Bags You Need

Work out how many bags of concrete a pour takes. Covers 40, 50, 60 and 80 lb bags plus 20, 25 and 30 kg, with bags-per-yard tables.

How much do you need?

Enter the volume, then pick the bag you are buying.

Enter a volume to see how many bags it takes.

All calculations run in your browser — nothing is sent anywhere.

How many bags of concrete formula

bags = volume ÷ yield per bag

Divide the volume you need by what one bag makes, then round up. An 80 lb bag yields about 0.6 ft³ and a 20 kg bag about 0.01 m³, so a cubic yard takes about 45 of the former and a cubic metre about 100 of the latter.

Worked example: 12 ft³ of concrete using 80 lb bags is 12 ÷ 0.6 = 20 bags, or 22 once you add the 10% buffer.

Bagged concrete is priced per bag but poured by volume, so every small job starts with the same question: how many bags is that? The answer depends entirely on bag size, and the difference is larger than people expect — a cubic yard is 45 bags at 80 lb but 90 at 40 lb.

Bags per cubic yard

Bag sizeYield per bagBags per yd³
80 lb0.60 ft³45
60 lb0.45 ft³60
50 lb0.375 ft³72
40 lb0.30 ft³90

Bags per cubic metre

Bag sizeYield per bagBags per m³
20 kg0.010 m³100
25 kg0.0125 m³80
30 kg0.015 m³67

Yields are the nominal figures printed on the bag. Real output moves slightly with water content and compaction, which is what the buffer is for.

Where bags stop making sense

Bags win on small and scattered work. Ready-mix wins on volume. The crossover sits around one cubic yard — roughly 45 × 80 lb bags — but the real limit is usually not cost, it is time and stamina.

The exception is work spread over scattered holes — a fence line, a run of deck footings — where a truck would spend most of its time waiting. There, bags stay sensible well past a cubic yard.

Mixing that many bags

Need the volume first? The cubic yard calculator goes from length, width and depth, and the cubic feet to cubic yards converter handles a figure you already have. To price the job, use the concrete cost calculator.

For shaped pours, the post hole calculator subtracts the post’s volume, and the Sonotube calculator covers round column forms — both are jobs where bags usually beat a truck.

Related concrete calculators

Pouring a different shape? These cover the rest of the common jobs.

Working out volumes on site?

This tool is web-only. The Concrete Calculator app covers the five volume calculators — rectangular and circular slabs, irregular slab area, circular columns and post holes — with saved projects, job history and full offline use.

Download on the App Store

Free · 4.8 ★ on the App Store

Frequently asked questions

How many bags of concrete are in a yard?
About 45 × 80 lb bags, 60 × 60 lb bags, 72 × 50 lb bags, or 90 × 40 lb bags. A cubic yard is 27 cubic feet, so divide 27 by the bag's yield — an 80 lb bag makes roughly 0.6 cubic feet, giving 45.
How many 20 kg bags make a cubic metre?
About 100. A 20 kg bag yields roughly 0.01 m³. A 25 kg bag yields about 0.0125 m³, so a cubic metre takes around 80, and 30 kg bags about 67.
When should I use bags instead of ready-mix?
Under about 1 cubic yard, or when the pour is broken into scattered small placements like fence posts, where a truck would be waiting around. Above roughly 1 cubic yard — about 45 × 80 lb bags — ready-mix is usually cheaper and very much faster.
How many bags can one person realistically mix?
Ten to fifteen 80 lb bags in a session is hard work with a wheelbarrow and a hoe; a powered mixer makes 30 or 40 manageable. Past that the concrete starts setting before you finish placing it, and quality suffers regardless of how strong you are.
Do bag yields vary?
Yes, a little. The figures here are the nominal yields printed on the bag, and real output shifts slightly with mix design, water content and how well it is compacted. That variation is exactly what the 10% buffer absorbs.
Should I buy a spare bag?
Always. Bags keep if stored dry and off the ground, and most suppliers take back unopened ones. Being a single bag short part-way through a pour means a cold joint or an unplanned trip, which costs far more than the spare.