How to use the Concrete Volume & Bag Calculator
Choose the shape and the units you’re measuring in. For a slab or footing, enter length, width and thickness in the same unit (6 inches is 0.5 ft). For a round column or post hole, enter the diameter and height. Set how many you’re pouring, the extra for waste, the bag size and prices. The green box shows the cubic yards to order and the rows show bags and costs.
Worked example
10 ft × 10 ft slab, 6 inches thick
| Volume: 10 × 10 × 0.5 | 50 cu ft |
| In cubic yards: 50 ÷ 27 | 1.85185 cu yd |
| With 10% extra | 2.04 cu yd (55 cu ft) |
| 80 lb bags at 0.60 cu ft each | 92 bags |
Assumptions and limits
- Bag yields are typical figures (80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45, 40 lb ≈ 0.30); check the bag you buy.
- The waste allowance covers spillage, uneven ground and forms; 5–10% is common.
- Rebar, gravel base and forms aren’t included.
Formula
Frequently asked questions
How many bags of concrete do I need for a 10×10 slab?
A 10 × 10 ft slab 4 inches thick is about 33 cu ft, or about 56 80-lb bags; at 6 inches it’s 50 cu ft, about 84 bags before waste.
Should I use bags or ready-mix?
Bags suit small jobs under about 1 cubic yard. For bigger pours, ready-mix delivery is usually cheaper and gives a stronger, more even slab.
Cite or link to this calculator
Using this calculator in an article, report or assignment? You can cite it like this:
CalcKite. (2026). Concrete Volume & Bag Calculator [Online calculator]. https://www.calckite.com/concrete-calculator/
Or add a link to it from your website or blog:
<a href="https://www.calckite.com/concrete-calculator/">Concrete Volume & Bag Calculator</a> by CalcKiteAdd this calculator to your website — free
Bloggers, schools, agents and businesses can embed the Concrete Volume & Bag Calculator on their own pages. Copy the code below and paste it into your page's HTML. The calculator resizes itself to fit, and works on phones.
Free to use — please keep the credit link under the calculator. Browse all free calculators for your website.
Results are estimates for information only and are not financial, tax or legal advice. Tax rules, interest rates and fees change, so confirm important numbers with your bank, employer or a qualified adviser. Read our disclaimer.