Bag count rises fast near one yard
One cubic yard is about 45 eighty-pound bags before waste. That is a lot of mixing, lifting, and water control for a single crew.
concrete
Concrete Bag Calculator
Convert slab dimensions into 40 lb, 60 lb, and 80 lb concrete bag counts.
Estimated concrete neededLength, width, and thickness are required before the estimate appears.
Example4 x 4 ft pad x 4 in = about 9 80 lb bags with 10% waste
Bag counts are rounded up. Check the exact yield on the product label before buying.
Last reviewed: May 12, 2026 by the BuilderCalc editorial team.
SSR formula reference
Concrete Bag Calculator formulas
These formulas are rendered in the server HTML so crawlers, LLMs, and users can read the method without running JavaScript. The interactive calculator can change the inputs, but the estimating math below is visible in the raw page source.
Volume (cubic feet) = Length x width x thickness (in inches / 12).
Volume (cubic yards) = Cubic feet / 27.
Bags (80-lb) = Cubic feet / 0.60, rounded up.
80-lb bag yields about 0.60 ft3, or 0.022 yd3.
| Result | Formula |
|---|---|
| Volume in cubic feet | Length x width x thickness in feet |
| Thickness in feet | Thickness in inches / 12 |
| Volume in cubic yards | Cubic feet / 27 |
| 80-lb bags | Cubic feet / 0.60, rounded up |
| Ready-mix order | Cubic yards x (1 + waste percent) |
Standard PSI by application
| Application | Recommended PSI |
|---|---|
| Patio or walkway | 3,000 PSI |
| Garage floor, residential | 3,500 PSI |
| Driveway, cars | 3,500 to 4,000 PSI |
| Driveway, trucks or RVs | 4,000 to 4,500 PSI |
| Foundations and footings | 3,000 to 4,000 PSI, per plan and code |
Bag yield reference
| Bag size | Common yield |
|---|---|
| 80-lb bag | About 0.60 ft3, or 0.022 yd3 |
| 60-lb bag | About 0.45 ft3, or 0.017 yd3 |
| 50-lb bag | About 0.375 ft3, or 0.0138 yd3 |
| 40-lb bag | About 0.30 ft3, or 0.011 yd3 |
Bag planning
Concrete Bag Calculator planning notes
Bag estimates are most useful for small pours, repairs, posts, and pads where delivery is not practical. Counts should include waste and always round up.
Use product yield as the final check
This calculator uses common yields, but each product label can differ. Check the exact bag yield before buying.
How to use it
Keep the estimate tied to field measurements
Calculate required volume
Enter project dimensions and waste so the required cubic feet are known before converting to bags.
Compare bag sizes
Use the 40, 50, 60, and 80 lb estimates to compare handling effort and total bag count.
Check product yield
Confirm the yield printed on the exact bag before buying, then round up to whole bags.
Related calculators
FAQ
Concrete estimating questions
How many 80 lb bags are in a cubic yard?
An 80 lb bag commonly yields about 0.60 cubic feet, so one cubic yard takes about 45 bags before waste.
When do bags stop being practical?
Bag mixing becomes labor-heavy near one cubic yard. At that size, compare bag cost and mixing time against ready-mix delivery and minimum fees.
Why does bag yield matter?
Different products and bag sizes yield different cubic feet. Use the product label as the final source before buying.
Should I round bag counts up?
Yes. Bag estimates should round up to whole bags after adding waste because partial bags are not practical for ordering.