Plan a retail premix purchase from actual bag yield.
Use this calculator for repairs, posts, steps, and other pours where packaged dry premix is more practical than delivered ready-mix.
Find cured or mixed yield on the exact product label or technical sheet. Bag weight alone does not establish volume because products and formulations differ.
Match the estimate to the purchasing decision.
Unlike ready-mix volume tools, this calculator divides adjusted pour volume by a retail product’s stated yield and rounds up. It does not convert bag weight into yield or compare labor against truck delivery.
Formula and calculation method.
Whole bags = ceiling(adjusted pour volume ÷ stated yield per bag)First calculate rectangular volume and add waste. Convert the entered bag yield from cubic feet or litres to the same volume basis, divide, then use the ceiling so a fractional requirement becomes the next whole bag.
Follow realistic concrete takeoffs.
Length 4 ft; width 4 ft; depth 4 in; yield 0.5 ft³; waste 10%
Working: 5.87 ft³ adjusted ÷ 0.5 ft³ = 11.73; round up
Result: 12 bags
Interpretation: Buying 11 bags would leave the modeled pour short even though the unrounded value is below 12.
Length 2 m; width 1.5 m; depth 10 cm; yield 20 L; waste 5%
Working: 315 L adjusted ÷ 20 L = 15.75; round up
Result: 16 bags
Interpretation: The count depends on the 20-litre label yield, not merely the package weight.
Turn the estimate into an order plan.
Treat the result as a purchase count for one specific product yield. Recalculate when changing product or bag size.
A large bag count may make ready-mix delivery more practical; compare access, minimum-load charges, mixing capacity, and placement time.
Assumptions and common mistakes.
What the estimate assumes
- Every bag has the stated volumetric yield.
- All bags are the same product and size.
- The pour is rectangular and constant-depth.
- Unused partial dry mix is not credited against another project.
Mistakes to avoid
- Entering bag weight instead of yield.
- Rounding the bag count down.
- Mixing litres and cubic feet.
- Ignoring placement time for many hand-mixed batches.
Handle unusual concrete plans explicitly.
No extra mathematical rounding occurs, though the selected waste is already included.
Any positive fraction of one bag still requires one whole bag.
A bag count cannot be calculated from package weight alone; obtain the manufacturer’s yield.
What this estimate leaves out.
The estimate does not account for partial-bag storage, batching loss beyond entered waste, water demand, mixing capacity, cure conditions, product suitability, strength specification, or the economics of ready-mix delivery.
Concrete planning questions.
Where do I find concrete bag yield?
Look for yield in cubic feet or litres on the bag label or manufacturer technical data sheet.
Why are concrete bags rounded up?
Retail bags are purchased whole, and rounding down would provide less than the modeled required volume.
Can I enter the bag weight?
No. Enter volumetric yield; equal-weight products can have different yields.
Does waste get added before bag rounding?
Yes. Waste increases required mix volume first, and the resulting quotient is then rounded up.
When should I consider ready-mix instead?
For a large count, compare delivery minimums, access, placement time, crew capacity, and total product cost with a supplier.