Concrete Floor Calculator: Garage & Basement Floors
This concrete floor calculator estimates the yards, bags and cost for garage, basement and interior floor slabs based on your floor area and thickness. Large flat pours leave little room for error, so a precise volume helps you order the right truck size and avoid a mid-pour shortfall.
Estimated concrete
Estimates only. Add ~5–10% for waste. Bag yields: 40 lb ≈ 0.30, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft. Concrete ≈ 150 lb per cu ft.
How the Concrete Floor Calculator works
- 1
Enter your dimensions
Type the length, width and thickness of your slab, footing or pad and choose your units, feet, inches or meters.
- 2
Get instant volume
See the result in cubic yards, cubic feet and cubic meters, plus weight, the moment you type, no page reloads.
- 3
Buy the right amount
We convert volume into the exact number of 40, 60 and 80 lb bags, truck loads and cost so you order without waste or shortfalls.
The formula
ft3 = Length_ft x Width_ft x (Thickness_in / 12); yd3 = ft3 / 27
- ·Length_ft = floor length (feet)
- ·Width_ft = floor width (feet)
- ·Thickness_in = slab thickness (inches)
- ·27 = cubic feet per cubic yard
- ·150 = pounds per cubic foot of concrete
Garage and interior floors are commonly 4 inches thick; a 5-6 inch pour suits heavier loads. A default 10% waste is added to the ordered volume.
Worked examples
Example 1: 20x20 ft garage floor, 4 in thick
- Volume = 20 x 20 x (4 / 12) = 133.3 ft3
- Cubic yards = 133.3 / 27 = 4.94 yd3
- Add 10% waste: 4.94 x 1.1 = 5.4 yd3
Result: about 5.4 cubic yards
Example 2: 24x24 ft garage floor, 5 in thick
- Volume = 24 x 24 x (5 / 12) = 240 ft3
- Cubic yards = 240 / 27 = 8.89 yd3
- With 10% waste: 8.89 x 1.1 = 9.8 yd3
Result: about 9.8 cubic yards
Concrete calculators by project type
Concrete bag yield & coverage
How much mixed concrete a standard bag yields, and how far a cubic yard goes at common slab depths.
| Bag size | Yield (cu ft) | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 | 90 |
| 60 lb | 0.45 | 60 |
| 80 lb | 0.60 | 45 |
- 40 lb
- 60 lb
- 80 lb
Related guides
Concrete floor calculator FAQs
How thick should a garage floor be?
A typical garage floor is poured 4 inches thick over a compacted base, which suits standard passenger vehicles. Go to 5–6 inches with rebar if you'll park heavy trucks, RVs or use a lift.
How many yards of concrete for a 20x20 garage floor?
A 20 ft × 20 ft floor at 4 inches thick is 400 × 0.333 = 133 ft³, or about 4.9 cubic yards. Add 5–10% for waste, so ordering about 5.5 yards is prudent.
Will one concrete truck cover my floor?
A full mixer truck carries about 10 cubic yards, which is enough for roughly an 800 ft² floor at 4 inches. Larger floors need multiple trucks scheduled back-to-back to keep the pour continuous.
Do I need a vapor barrier under a basement or interior floor?
Yes, a 6-mil-or-thicker poly vapor barrier under interior and basement floors blocks ground moisture that can damage flooring above. It's inexpensive insurance against dampness and mold.
How much does a concrete floor cost per yard?
Ready-mix runs about $125–$165 per cubic yard delivered, before base prep, reinforcement, finishing and labor. On large floors, per-yard pricing often improves with full-truck loads.
Should I use rebar or wire mesh in a floor slab?
Welded wire mesh controls shrinkage cracking in typical residential floors, while rebar is added for garages and areas carrying heavier loads. Many garage floors use both mesh and a grid of rebar for durability.
How many bags of concrete would a 12x12 floor take?
A 12x12 ft floor at 4 inches is 12 x 12 x (4/12) = 48 ft3, which is about 80 eighty-lb bags. That much bagged mix is impractical, so a floor this size is far cheaper and faster with a ready-mix truck.
What slope should a garage floor have?
Pitch the floor about 1/8 inch per foot toward the overhead door so water and melting snow drain out. A dead-level garage floor tends to pond water near the back wall.
Do I need control joints in a concrete floor?
Yes. Cut or tool control joints so they are spaced in feet at roughly 2 to 3 times the slab thickness in inches, so a 4 inch floor gets joints every 8 to 10 feet. Joints give cracks a planned place to form.
How long before I can park on a new garage floor?
Foot traffic is fine after 24 to 48 hours, but wait about 7 days before driving a car onto it and closer to 28 days before parking heavy vehicles or storing heavy equipment.
How thick should a basement or interior floor be?
Non-structural interior and basement floors are typically 3.5 to 4 inches thick over a compacted base and vapor barrier. Thicker pours are reserved for areas that carry vehicles or heavy machinery.
Should I use fiber mesh or wire mesh in a floor?
Both help control shrinkage cracking. Wire mesh or rebar placed at mid-depth gives better structural crack control for slabs that carry vehicles, while fiber mesh mixed into the concrete is convenient for lightly loaded interior floors.
Do I need insulation under a heated floor?
Yes, if you are installing radiant heat, place rigid foam insulation under the slab so heat rises into the room instead of into the ground. This dramatically improves efficiency and warm-up time.