How to Calculate Cubic Feet
Calculating cubic feet is straightforward: you multiply three dimensions — length, width, and height — to get volume. The tricky part is making sure all three measurements use the same unit before you multiply. Mix feet with inches, and you'll get an answer that's 12 times too large (or too small).
(all dimensions in feet)
OR
Cubic feet = (L × W × H in inches) ÷ 1,728
(since 12³ = 1,728 cubic inches per cubic foot)
Our calculator handles the unit conversion automatically — type in inches, yards, meters, or centimeters and we convert to feet under the hood. If you're doing the math manually with mixed units, always normalize everything to feet first.
Worked example: a moving box
Suppose you're measuring a moving box that's 24 inches long × 18 inches wide × 12 inches tall and you want the volume in cubic feet:
- Convert each side to feet: 24 ÷ 12 = 2 ft, 18 ÷ 12 = 1.5 ft, 12 ÷ 12 = 1 ft
- Multiply: 2 × 1.5 × 1 = 3 cubic feet
- Or in one step: (24 × 18 × 12) ÷ 1,728 = 5,184 ÷ 1,728 = 3 ft³
When You Need to Calculate Cubic Feet
Cubic feet show up everywhere in daily life and project planning. Here are the most common scenarios where this calculator helps.
Appliance shopping
Refrigerators, freezers, microwaves, and ovens are all sold by interior cubic feet capacity. A standard top-freezer fridge is 14–22 ft³; French-door models run 22–28 ft³; counter-depth units are slightly smaller (18–25 ft³) for the same exterior footprint. To check if a replacement fits in your existing space, measure the cabinet opening and convert to cubic feet to compare with appliance specs.
Moving and shipping
Moving truck rental and shipping companies quote capacity in cubic feet. A small moving truck holds around 300 ft³ (about 1 room); a standard 17-foot truck holds 1,000 ft³ (2-3 bedrooms); a 26-foot truck holds 1,700 ft³ (full house). Shipping containers: a 20-foot container is ~1,170 ft³, a 40-foot container is ~2,390 ft³.
Mulch and landscape materials
Bagged mulch is sold in 2 cubic foot bags almost universally in the US. To cover a 100 sq ft bed at 3 inches deep, you need 25 cubic feet (12.5 bags). At 4 inches deep, you need 33 ft³ (17 bags). The math: square feet × (depth ÷ 12) = cubic feet of mulch needed.
Garden beds and planters
Raised garden beds need soil calculated in cubic feet. A 4 × 8 ft bed at 12 inches deep holds 32 cubic feet of soil. Planters for indoor plants typically need 0.5 to 5 cubic feet of potting mix depending on size. Bagged potting soil comes in 1 ft³, 1.5 ft³, and 2 ft³ bags most commonly.
Concrete and footings
Smaller concrete projects — sonotube footings, fence post holes, small slabs — are often sized in cubic feet rather than yards. A standard 60 lb bag of concrete mix yields about 0.45 ft³ of concrete; an 80 lb bag yields 0.6 ft³. For larger projects, convert to cubic yards (÷ 27) and order ready-mix delivery.
Air handling and HVAC
Room volume in cubic feet is critical for sizing air conditioners, heaters, dehumidifiers, and ventilation fans. A standard 12 × 12 ft bedroom with 8 ft ceilings is 1,152 ft³. HVAC manufacturers list capacity in BTU/hr; rule of thumb is 20 BTU per square foot or roughly 2.5 BTU per cubic foot for residential rooms.
Water tanks and fish tanks
Aquariums and water storage tanks list capacity in gallons, but you can calculate volume in cubic feet and convert: 1 cubic foot of water = 7.48 US gallons. A 55-gallon aquarium holds 7.35 ft³ of water (which weighs about 458 lb — important for floor structure).
How Big Is a Cubic Foot? Visualization Guide
One cubic foot is a 12-inch cube — picture a basketball lightly inflated, or a sturdy moving box. Some useful comparisons:
- ~7.48 US gallons of liquid, or about 28.3 liters
- 1,728 cubic inches — the same as a 12 × 12 × 12 inch box
- 0.037 cubic yards (so it takes 27 cubic feet to equal one cubic yard)
- 0.0283 cubic meters
- Visualization: roughly a microwave oven's interior, or 6 standard milk gallons stacked
- Weight when filled: water = 62.4 lb, dry sand = ~100 lb, gravel = ~95 lb, concrete = ~150 lb
Cubic Feet Conversion Table
Quick reference for the most common conversions between cubic feet and other volume units:
| 1 Cubic Foot equals... | Conversion factor | Example use |
|---|---|---|
| Cubic yards | 0.037 yd³ | Bulk landscape orders |
| Cubic meters | 0.0283 m³ | International shipping |
| Cubic inches | 1,728 in³ | Small parts, electronics |
| US gallons | 7.4805 gal | Liquid storage, fish tanks |
| Imperial gallons | 6.229 gal | UK/Canadian projects |
| Liters | 28.3168 L | Metric conversions |
| Quarts (US) | 29.92 qt | Smaller liquid amounts |
| Bushels | 0.804 bu | Agriculture, grain storage |
Formulas for Common Shapes
Most real-world objects aren't perfect rectangular prisms. Here are the formulas for the next most common shapes — all expressed in cubic feet.
Rectangular box (prism)
Cylinder (round tank, post, column)
(where radius = diameter ÷ 2)
Example: a 3-foot diameter water tank that's 6 feet tall. Radius = 1.5 ft. Volume = 3.14159 × 1.5² × 6 = 42.4 cubic feet (≈ 317 gallons).
Sphere (round tanks, balls)
Example: a 5-foot diameter spherical tank. Radius = 2.5 ft. Volume = 1.333 × 3.14159 × 2.5³ = 65.4 cubic feet.
Cone (funnels, conical piles)
Trapezoidal prism
Common Cubic Feet Reference: Mulch, Soil, Concrete Bags
Bagged products are usually sold by cubic feet, so knowing standard bag sizes helps you order without doing too much math.
| Product | Standard bag size | Coverage at typical depth |
|---|---|---|
| Mulch (shredded) | 2 ft³ | 12 sq ft @ 2" / 8 sq ft @ 3" |
| Mulch (premium / cedar) | 2 ft³ or 3 ft³ | varies |
| Potting soil | 1, 1.5, or 2 ft³ | fills small to medium containers |
| Topsoil | 0.75 or 1 ft³ | 3 sq ft @ 3" |
| Compost | 1 or 2 ft³ | — |
| Sakrete / concrete mix (60 lb) | 0.45 ft³ wet | — |
| Quikrete (80 lb) | 0.6 ft³ wet | — |
| Pea gravel (bag) | 0.5 ft³ | 3 sq ft @ 2" |
| Sand (50 lb) | 0.5 ft³ | — |
Cubic Feet for Moving and Storage
Moving truck capacity is the cubic foot calculation everyone wishes they'd done before loading the truck. Here's what you actually fit in standard sizes:
| Truck size | Cubic feet | Typical capacity |
|---|---|---|
| 10 ft truck | 402 ft³ | Studio or 1-bedroom |
| 15 ft truck | 764 ft³ | 1-2 bedrooms |
| 17 ft truck | 865 ft³ | 2 bedrooms |
| 20 ft truck | 1,016 ft³ | 2-3 bedrooms |
| 26 ft truck | 1,700 ft³ | 3-4 bedrooms / whole house |
| 20 ft shipping container | 1,170 ft³ | 2 bedrooms / international |
| 40 ft shipping container | 2,390 ft³ | 3-5 bedrooms / international |
| 5x5 storage unit | 200 ft³ | Small closet contents |
| 10x10 storage unit | 800 ft³ | 1-2 bedrooms |
| 10x20 storage unit | 1,600 ft³ | 3-4 bedrooms |
Common Mistakes
- Mixing feet and inches — the #1 error. Convert everything to one unit first.
- Confusing square feet and cubic feet — square feet is area (2D), cubic feet is volume (3D). A 100 sq ft room with 8-ft ceilings is 800 cubic feet of space.
- Using exterior dimensions for interior capacity — for appliances and containers, measure the inside, not the outside.
- Forgetting taper or curve — for cylindrical tanks with conical bottoms, use the cylinder + cone formula separately and add the results.
- Ignoring the difference between dry and wet volume — bagged concrete is sold dry; the wet volume after mixing is ~75% of the dry weight bag rating.