Concrete Bag Calculator
Buying bagged concrete? Enter your dimensions and bag size to see exactly how many bags to buy — no more guessing at the hardware store or running short halfway through.
Floors, pads, patios, driveways — flat rectangular pours.
How many bags of concrete per project
The formula
Each bag yields a fixed volume of mixed concrete. Divide your total volume by the bag's yield and round up. The calculator does this for every common bag size.
- 80 lb bag ≈ 0.60 ft³ (0.017 m³) of set concrete.
- 60 lb bag ≈ 0.45 ft³ (0.013 m³).
- 40 lb bag ≈ 0.30 ft³ (0.0085 m³).
- Rule of thumb: ~60 × 80 lb bags fill one cubic yard.
Worked example
Setting 6 fence posts in 10 in × 24 in holes:
- One hole (round) = π × (5 in)² × 24 in ≈ 1,885 in³ = 1.09 ft³.
- Six holes = 6.5 ft³.
- At 0.60 ft³ per 80 lb bag → 6.5 ÷ 0.6 = 11 bags.
Buy about 11 × 80 lb bags (add a couple as spares).
Sizing, thickness & waste
Which bag size?
- 80 lb bags: fewest bags to carry, best for slabs and footings.
- 60 lb bags: a manageable compromise for most DIY work.
- 40 lb bags: lighter to lift but you'll need far more of them.
When bags stop making sense
Bagged concrete is convenient up to roughly 0.5 m³ (about 30 × 80 lb bags). Beyond that the cost and labour add up fast — ready-mix or a small site mixer becomes the better call.
What produces this much concrete?
Past a certain point, mixing from bags is slow. Here's what scales better:
Small pour — mix on site
Under ~0.5 m³ (≈0.65 yd³) you can mix on site from bags. A portable mixer saves time over hand-mixing once you pass a few bags.
Medium pour — small mixer or ready-mix
From ~0.5–2 m³, a small or self-loading mixer keeps you independent of delivery schedules; otherwise order ready-mix.
Large pour — self-loading mixer or delivery
At 2–10 m³, compare ready-mix delivery against a self-loading mixer or mixer truck if you pour regularly.
On-site batching becomes economical
Above ~10 m³, repeated or remote pours usually cost less with on-site batching than per-load delivery. A mobile or compact plant sets up fast.
Continuous production — dedicated plant
Beyond ~50 m³ per job, a stationary or ready-mix plant delivers the throughput and consistency large projects need.
Frequently asked questions
How many bags of concrete do I need?
Divide your total concrete volume by the yield of one bag and round up. An 80 lb bag yields about 0.60 ft³, a 60 lb bag 0.45 ft³, and a 40 lb bag 0.30 ft³. Enter your dimensions above to get the exact count.
How do you calculate bags of concrete?
Work out the pour volume (length × width × thickness), then divide by the chosen bag's yield and round up. The calculator above does this for 40, 60 and 80 lb bags and metric 20/25/40 kg bags.
How many 80 lb bags make a yard of concrete?
About 60 × 80 lb bags make one cubic yard of usable concrete. (A cubic yard is 27 ft³; allowing for waste each 80 lb bag delivers roughly 0.45 ft³ in place.)
How many 60 lb bags make a yard of concrete?
Roughly 90 × 60 lb bags fill a cubic yard. For 40 lb bags you would need about 133 bags — which is why bags stop being practical for large pours.
How many bags of concrete are in a cubic metre?
Roughly 78 × 80 lb bags, 104 × 60 lb bags, or about 87 × 25 kg bags fill one cubic metre of set concrete.
When should I stop using bags and use ready-mix?
Bagged concrete is convenient up to about 0.5 m³ (roughly 30 × 80 lb bags). Past 80–100 bags the cost and mixing labour add up fast — ready-mix delivery or an on-site mixer is usually cheaper and faster.
Can a portable mixer handle this volume?
A portable drum mixer comfortably handles up to a few cubic metres a day, batch by batch. For larger or continuous pours, step up to a self-loading mixer or a mobile batching plant — see the equipment guide above.
How much extra concrete should I order for waste?
Add 5–10% to your calculated volume to cover spillage, uneven subgrade, and over-excavation. For small or irregular pours, 10% is safer because running short mid-pour creates a cold joint.