The Formula
ft³ = ft² × (depth in inches ÷ 12)
ft³ = ft² × depth in feet
yd³ = ft³ ÷ 27
Volume calculator
Square Feet to Cubic Feet Calculator
Square feet alone cannot tell you how much concrete, soil, mulch, or gravel to order. You also need the depth. Enter the area in ft², add the thickness in inches or feet, and this calculator will turn that flat surface into a real volume in cubic feet and cubic yards. If you still need to measure the area itself, start with our square footage calculator.
Need the base surface area first? Open the square footage calculator before you estimate the volume.
Square Feet to Cubic Feet Calculator
This is a two-step volume calculation: enter the surface area first, then tell the calculator how deep the material will be.
Step 1
Step 2
Result
Cubic Feet
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Cubic Yards
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Formula
ft³ = ft² × (depth in inches ÷ 12)
How to Convert Square Feet to Cubic Feet
How to Convert Square Feet to Cubic Feet
Why You Need a Depth Measurement
Square feet measures a flat surface. Cubic feet measures volume. Without a thickness, height, or depth, there is no third dimension, so the conversion cannot happen.
Step-by-Step Example
A 10 × 10 slab is 100 ft². At 4 inches deep, the depth becomes 4 ÷ 12 = 0.3333 ft. Multiply 100 × 0.3333 and you get 33.33 ft³, which is about 1.23 yd³.
Material depth guide
Depth Reference Guide
Most users know the area but hesitate on the thickness. These common depth ranges give you a practical starting point for concrete, soil, mulch, and base materials.
| Material | Recommended Depth | Why It Matters |
|---|---|---|
| Concrete slab | 4 inches | Standard residential driveway and sidewalk thickness. |
| Concrete (heavy load) | 6 inches | Useful for garage floors and areas with heavier equipment loads. |
| Mulch | 2–3 inches | A common garden coverage depth for moisture control and weed suppression. |
| Topsoil | 4–6 inches | A practical minimum range for lawn repair and basic planting beds. |
| Gravel base | 4–6 inches | Typical for drainage layers, paver prep, and compacted support beds. |
| Sand | 1–2 inches | Often used as a leveling layer under pavers or other surface finishes. |
| Rubber mulch | 3–4 inches | A common playground safety depth depending on the fall-height target. |
| Snow | Measure actual depth | For snow removal estimates, the measured depth matters more than a standard rule. |
Volume table
Cubic Feet at Common Depths
Click any row to load that area into the calculator above.
These rows use correct depth math for 2-inch, 4-inch, and 6-inch material layers. Load any area directly into the calculator, then change the depth if your project uses a different thickness.
| Area (ft²) | 2 inches deep | 4 inches deep | 6 inches deep |
|---|---|---|---|
| 10 ft² | 1.67 ft³ | 3.33 ft³ | 5.00 ft³ |
| 25 ft² | 4.17 ft³ | 8.33 ft³ | 12.50 ft³ |
| 50 ft² | 8.33 ft³ | 16.67 ft³ | 25.00 ft³ |
| 100 ft² | 16.67 ft³ | 33.33 ft³ | 50.00 ft³ |
| 150 ft² | 25.00 ft³ | 50.00 ft³ | 75.00 ft³ |
| 200 ft² | 33.33 ft³ | 66.67 ft³ | 100.00 ft³ |
| 300 ft² | 50.00 ft³ | 100.00 ft³ | 150.00 ft³ |
| 400 ft² | 66.67 ft³ | 133.33 ft³ | 200.00 ft³ |
| 500 ft² | 83.33 ft³ | 166.67 ft³ | 250.00 ft³ |
| 750 ft² | 125.00 ft³ | 250.00 ft³ | 375.00 ft³ |
| 1,000 ft² | 166.67 ft³ | 333.33 ft³ | 500.00 ft³ |
| 1,500 ft² | 250.00 ft³ | 500.00 ft³ | 750.00 ft³ |
| 2,000 ft² | 333.33 ft³ | 666.67 ft³ | 1000.00 ft³ |
Use cases
Common Use Cases
Concrete slabs and flatwork
This is the classic use case: a driveway, patio, sidewalk, shed pad, or slab where you already know the area in ft² and need the pour volume.
Because suppliers usually quote concrete in cubic yards, showing yd³ alongside ft³ saves the extra divide-by-27 step.
Soil, topsoil, and fill
Garden beds, lawn repair, grading, and backfill often start as a surface area and a target depth.
That makes ft² plus thickness the fastest way to estimate how much soil or fill material to order.
Mulch and landscape coverage
Mulch is usually spread at 2 to 3 inches, so a shallow depth can still create a surprisingly large volume.
This calculator helps you move from bed area to bag or bulk-order planning without doing the inch-to-foot math by hand.
Gravel, sand, and base layers
Paver bases, drainage trenches, and compacted support layers are often specified by thickness rather than by total volume.
Once the area is measured, cubic feet and cubic yards become the ordering numbers that suppliers care about.
HVAC, storage, and enclosure volume
The same area-times-height logic applies when the depth is really a room height or enclosure height.
That makes the calculator useful for rough airflow, storage, and cubic-space planning when the floor area is already known.
If your project moves from area-based shopping into deeper material planning, the concrete calculator is the natural next step. For related area conversions, you can also jump to square feet to square yards or compare land-sized surfaces with square feet to acres.
FAQ
Frequently Asked Questions
How do I convert square feet to cubic feet?1
You need both area and depth. The core formula is cubic feet = square feet × depth in feet. If the depth is given in inches, divide the inches by 12 first, then multiply by the square-foot area.
How many cubic feet is 100 square feet at 4 inches deep?2
100 square feet at 4 inches deep equals 33.33 cubic feet because 4 inches is 0.3333 feet, and 100 × 0.3333 = 33.33 ft³.
How do I convert cubic feet to cubic yards?3
Divide cubic feet by 27. That is why this calculator also shows cubic yards automatically, because many concrete, soil, and mulch orders in the United States are quoted in yd³ instead of ft³.
How much concrete do I need for a 10×10 slab at 4 inches?4
A 10×10 slab is 100 square feet. At 4 inches deep, that becomes 33.33 cubic feet. Divide by 27 and you get about 1.23 cubic yards. If you need mix totals or overage planning, use the concrete calculator next.
Open the concrete calculatorCan I convert square feet to cubic feet without knowing the depth?5
No. Square feet is a 2D area measurement, while cubic feet is a 3D volume measurement. Without depth, thickness, or height, there is no third dimension, so the conversion cannot be completed.
How many cubic feet of mulch do I need for 200 square feet?6
If you spread mulch 3 inches deep, 200 square feet needs 50.00 cubic feet because 3 inches is 0.25 feet, and 200 × 0.25 = 50 ft³.