Construction Calculator
Concrete Bag Calculator
Estimate how many bags of concrete you need for slabs, patios, post holes, pads, footings, walkways, fence posts, deck posts, and small concrete jobs. Choose common 40 lb, 50 lb, 60 lb, and 80 lb bag sizes or enter a custom yield.
Best for
Small concrete jobs
Outputs
Bags, yards, cost
Audience
DIY + contractors
Quick estimate
Bagged concrete is usually best for smaller pours. For larger jobs, compare the total bag count and labor against ready-mix delivery.
Common rule of thumb
45 bags of 80 lb concrete ≈ 1 cubic yard
Calculate concrete bags
Choose a project type, enter dimensions, select a bag size, and estimate the number of bags, cubic yards, waste-adjusted volume, and material cost.
Concrete bag estimate
Recommended bags
62
Based on 80 lb bag and 10% waste.
Bag yields vary by brand and mix type. Check the bag label before ordering, and round up so the pour is not interrupted.
Concrete bag yields
40 lb bag: about 0.30 cubic feet
50 lb bag: about 0.375 cubic feet
60 lb bag: about 0.45 cubic feet
80 lb bag: about 0.60 cubic feet
Formula used
Volume is calculated as length × width × depth. The calculator converts depth from inches to feet, converts cubic feet to cubic yards, adds waste, then divides by the selected bag yield.
When to use ready-mix
If the estimate requires hundreds of bags, ready-mix concrete may be more practical. Use this calculator to compare bag count, material cost, and labor before buying.
Concrete bag calculator FAQs
How many bags of concrete do I need?
Measure the project length, width, and depth. Convert depth to feet, multiply length × width × depth, then divide by the concrete bag yield. Add waste so you do not run short during the pour.
How many 80 lb bags make a cubic yard?
About 45 bags. An 80 lb bag usually yields about 0.6 cubic feet, and one cubic yard contains 27 cubic feet.
Is bagged concrete good for slabs?
Yes, for small slabs, pads, post holes, and repairs. For larger slabs, bagged concrete can become expensive and labor-heavy compared with ready-mix delivery.
How much waste should I add?
A 5% to 10% waste factor is common. Use more if the base is uneven, the formwork is irregular, or the excavation depth varies.