How many bags of concrete do I need for a 10 × 6 ft slab, 4 inches thick?
For the worked example (10 × 6 ft slab, 4 in thick) the material list is Concrete mix: 37 × 80 lb bags (calculated 36.67 × 80 lb bags, based on 0.6 cu ft per bag, 10% allowance). Quantities to buy are whole units rounded up from the calculated amounts. Enter your own measurements in the calculator above for your exact list.
How to use this calculator
- Measure the slab length and width, and decide on the thickness.
- Keep or change the extra allowance. 10% is a starting value, not a rule.
- Pick the bag size you plan to buy.
- Read the cubic-yard figure if you are comparing ready-mix delivery, or the bag count if you are buying bags.
- Copy, print or share the material list.
How this is calculated
- Volume (cu ft) = length (ft) × width (ft) × thickness (ft), with thickness in inches ÷ 12
- With allowance = volume × (1 + allowance ÷ 100)
- Cubic yards = cubic feet ÷ 27
- Bags = round up (volume with allowance ÷ yield per bag)
Geometry is deterministic. Material coverage, density, installation waste and product yield can vary. We expose those assumptions so you can replace them with the values printed on the products you are actually buying. Treat every result as an estimate. Items on your list are labelled Calculated (straight from your measurements) or Estimated (depends on an assumption), and “Buy” quantities are whole units rounded up.
Sources
- QUIKRETE – Concrete Mix data sheet. Approximate yields: 40 lb → 0.30 cu ft, 50 lb → 0.375 cu ft, 60 lb → 0.45 cu ft, 80 lb → 0.60 cu ft (some copies of the sheet list only 40, 60 and 80 lb). Other mixes (for example fast-setting) have different yields. Use the yield printed on the mix you are actually buying.
Last reviewed: . See the methodology.
Assumptions
These starting values are used until you change them. They are typical, not universal. Check the label on the product you are buying.
| Assumption | Starting value | Where it comes from |
|---|---|---|
| Cubic feet in a cubic yard | 27 | Mathematical – 3 ft × 3 ft × 3 ft |
| Inches in a foot | 12 | Mathematical – Depth in inches ÷ 12 gives feet |
| Yield per bag (QUIKRETE Concrete Mix) | 40 lb 0.30 · 50 lb 0.375 · 60 lb 0.45 · 80 lb 0.60 cu ft | Manufacturer / industry sourced – Approximate. Use the yield printed on the mix you buy. |
| Extra allowance | 10% | Common planning default |
| Custom bag yield (optional) | You enter it | You enter it (product / supplier) |
Worked example
A 10 × 6 ft slab, 4 in thick, with a 10% allowance and 80 lb bags (0.60 cu ft each):
- Concrete mix: 37 × 80 lb bags (22 cu ft to fill (0.81 yd³)) · 0.6 cu ft per bag, 10% allowance
Common questions
How thick should my slab be?
This tool does not make design recommendations. The 4 in and 6 in buttons are only common quick values. Thickness, base and reinforcement depend on your project, soil and local requirements.
Why round bags up?
Running short mid-pour is worse than having a bag left over, so bag counts are always rounded up to whole bags.
When is ready-mix worth comparing?
For larger pours, delivered ready-mix may be worth a quote. Enter your own prices to compare material-only cost. Delivery, pump, short-load fees and labour are not included unless you add them yourself.
Guides
- How Much Concrete Do I Need for a Slab?Turn slab dimensions into volume and an order quantity.
- How Many Bags of Concrete Do I Need?Turn a volume into bag counts, and bags into cubic yards.
- 4-Inch vs 6-Inch Concrete Slab: How Much More Concrete?How thickness changes the volume of concrete for the same slab area.
- How Many Fence Posts and Pickets Do I Need?Posts, rails and pickets from run length, spacing, picket width and gap.
- How Fence Post Spacing Changes Your Material CountPosts, rails and pickets at three post spacings for the same fence.