Concrete Bag Calculator

Buying bagged concrete at Home Depot or Lowe’s? Enter your project dimensions and this calculator shows how many bags you need in every common size — 40, 50, 60, and 80 lb — so you can compare and load the right number on the cart.

Length

Width

Thickness

Quantity

Waste factor

Bag size

Pin it

Total volume required

0.43Cubic Yards

Cubic feet

11.73

Cubic meters

0.33

Bags (80 lb)

Bags by size

40 lb

50 lb

60 lb

80 lb

Estimate includes your waste factor. Figures are estimates, not a quote.

Concrete Bag Calculator — estimate
Shape: Slab
Units: imperial
Waste factor: 10%
Estimated volume: 11.73 cubic feet
Cubic yards: 0.43
Bags (80 lb): 20

This is an estimate, not a quote. Verify with your supplier.

How to use this calculator

1Enter the length, width, and thickness of your pour (or a single small footing or pad).
2Add a waste factor — 10% covers the partial bag you almost always lose.
3Read the bag count for your preferred size, or use the side-by-side comparison to see all four sizes at once.
4Round up — you cannot buy a fraction of a bag, and the calculator already does this for you.

Formula & rounding

Bags = waste-adjusted cubic feet ÷ bag yield, rounded up. Yields are about 0.60 cf for an 80 lb bag, 0.45 cf for 60 lb, 0.375 cf for 50 lb, and 0.30 cf for 40 lb. Yields vary by brand and mix, so results are estimates.

8 ft × 4 ft walkway, 4 inches thick

Volume = 8 × 4 × (4 ÷ 12) = 10.67 cubic feet
With 10% waste: 10.67 × 1.10 = 11.73 cubic feet
80 lb bags = 11.73 ÷ 0.60, rounded up = 20 bags
60 lb bags = 11.73 ÷ 0.45, rounded up = 27 bags

= 20 × 80 lb bags, or 27 × 60 lb bags

1 cubic yard bag-count check

1 cubic yard = 27 cubic feet before waste
80 lb bags = 27 ÷ 0.60, rounded up = 45 bags
60 lb bags = 27 ÷ 0.45, rounded up = 60 bags
Dry mix weight at 45 × 80 lb = about 3,600 lb before water

= ≈45 × 80 lb bags per cubic yard, which is usually ready-mix territory

Concrete bag yield table

Use the yield printed on your bag when it differs from this table. These planning values let you compare bag sizes before you load a cart or schedule a delivery.

Bag size	Approx. yield	Bags per yd³	Best fit
40 lb	≈0.30 cu ft	≈90	Small repairs, narrow holes, easier lifting
50 lb	≈0.375 cu ft	≈72	Post holes and small pads
60 lb	≈0.45 cu ft	≈60	Hand-mixing balance of weight and yield
80 lb	≈0.60 cu ft	≈45	Fewer bags for pads and larger pours

Estimate · unofficial. Yields vary by brand and mix; always round bag counts up.

Frequently asked questions

How many bags of concrete do I need?

Divide your waste-adjusted volume (in cubic feet) by the yield of the bag size and round up. An 80 lb bag covers about 0.60 cubic feet, so a 12-cubic-foot job needs about 20 bags. Enter your dimensions to get the exact count.

How many 80 lb bags of concrete are in a cubic yard?

A cubic yard is 27 cubic feet. At roughly 0.60 cubic feet per 80 lb bag, that is about 45 bags per cubic yard — before any waste factor. For 60 lb bags it is about 60 per yard.

What size concrete bag should I buy?

Bigger bags (80 lb) mean fewer bags to carry and mix but more weight per bag. Smaller bags (40–50 lb) are easier to handle. The comparison table shows the count for each so you can trade off weight against quantity.

When should I switch from bags to ready-mix?

Mixing more than about 1 cubic yard (≈45 × 80 lb bags) by hand is slow and tiring. At that point a ready-mix delivery is usually faster and often cheaper. Ask suppliers about minimum orders and short-load fees before deciding.

How heavy is a cubic yard of bagged concrete?

At roughly 45 bags of 80 lb mix, one cubic yard is about 3,600 lb of dry bags before water. That is more than many homeowners want to load, unload, and hand-mix, and it may exceed a light pickup payload.

Assumptions & sources

Bag yields: ≈0.30 / 0.375 / 0.45 / 0.60 cu ft for 40 / 50 / 60 / 80 lb bags (planning estimates — the yield printed on the bag is authoritative and varies by brand/mix).
Bags per cubic yard: ≈90 / 72 / 60 / 45 bags (40 / 50 / 60 / 80 lb) to fill 27 cu ft.
Handling weight: One cubic yard is about 45 × 80 lb bags, or roughly 3,600 lb of dry mix before water; confirm pallet count and vehicle payload before pickup.
Waste factor: Default 10%; bag counts always round up (you cannot buy part of a bag).
When to switch: Above ~1 cubic yard (≈45 × 80 lb bags) ready-mix is usually cheaper and far less mixing.

See the methodology & sources for how these values, formulas, and rounding are chosen.

Helpful concrete guides

Concrete bag sizes & yields — compares 40, 50, 60, and 80 lb bags, pallet counts, and when ready-mix becomes the better buy.
How to calculate concrete — shows how the cubic-foot volume becomes bags after waste factor and rounding.

This is an estimate, not a quote. Concrete quantities, bag yields, block coverage, and prices vary with product, brand, mix, region, supplier, tax, delivery, and on-site conditions. Always confirm with your supplier and round up for safety. For structural or code-related work, consult a qualified professional or your local building authority.