Square Feet to Cubic Feet Calculator
Area can't become volume without a depth. Enter your square footage and a depth in inches to get cubic feet, cubic yards, and tons for mulch, concrete, gravel, soil, or sand.
Last updated:Material: Mulch 3" — tons use loose delivered density in lb/ft³: wood chips 16.3 (EPA 440 lb/yd³), concrete 150 (PCA), crushed stone 100 (EPA), topsoil 95. Every source and its caveat is listed in Sources.
How the Conversion Works
Unit factors follow NIST Special Publication 811 and the Federal Register definition of the foot; densities are cited in Sources below.
cubic feet = square feet × (depth in inches ÷ 12)
cubic yards = cubic feet ÷ 27 · tons = cubic feet × density ÷ 2,000
And back the other way, which is what you need when a load has already been delivered:
square feet = cubic yards × 27 ÷ depth in feet · depth in inches = cubic yards × 27 ÷ square feet × 12
Only the density is not geometry. Area and depth fix the volume exactly; the tonnage depends on how heavy the material is per cubic foot, which is why the presets matter more than the arithmetic. Area alone can never produce a volume — see square feet vs cubic feet for when each unit applies.
Worked Example
A 20 ft × 20 ft patio slab, 4 inches thick. How much concrete, and how is it ordered?
- Area: 20 × 20 = 400 sq ft.
- Depth in feet: 4 ÷ 12 = 1/3 ft. So cubic feet = 400 ÷ 3 = 133.33 ft³.
- Cubic yards: 133.33 ÷ 27 = 4.9383 yd³. At 4 inches the shortcut is exact — one cubic yard covers 81 sq ft, and 400 ÷ 81 = 4.9383. ✓
- Add waste for spill, form spread and subgrade irregularity: 4.9383 × 1.05 = 5.185 yd³.
- Order in the increments ready-mix is sold in: 5.25 yd³. Rounding to the nearest yard (5.00) leaves you 0.19 yd³ short — about 15 sq ft of slab at 4 inches.
- Weight check: 133.33 ft³ × 150 lb/ft³ ÷ 2,000 = 10.0 tons of normal-weight concrete in the finished slab. That is a load-bearing number for the subgrade, not an order quantity — you order yards.
Same arithmetic, different material: a gravel path 3 ft × 40 ft = 120 sq ft at 4 inches is 120 ÷ 3 = 40 ft³ = 1.4815 yd³, so order 1.5 yd³, which weighs 40 × 100 ÷ 2,000 = 2.0 tons as delivered loose.
Coverage per cubic yard, by depth
One cubic yard is 27 cubic feet, so the area it covers is 27 ÷ depth in feet. That is the fastest way to sanity-check an order without touching the calculator: sq ft per yd³ = 324 ÷ depth in inches.
| Depth | Depth in feet | Sq ft covered by 1 yd³ |
|---|---|---|
| 1 in | 0.0833333 | 324 |
| 2 in | 0.1666667 | 162 |
| 3 in | 0.25 | 108 |
| 4 in | 0.3333333 | 81 |
| 5 in | 0.4166667 | 64.8 |
| 6 in | 0.5 | 54 |
| 8 in | 0.6666667 | 40.5 |
| 12 in | 1 | 27 |
Two of these are worth memorising because they terminate: 3 in → 108 sq ft per yard (mulch) and 6 in → 54 sq ft per yard (gravel base). The 4-inch figure, 81 sq ft per yard, is exact too but comes from 1/3 ft, so cubic feet land on a repeating decimal even though the yard coverage does not.
What is a cubic foot?
A cubic foot is the volume of a cube one foot on each edge: 12 in × 12 in × 12 in = 1,728 cubic inches. In metric it is exact rather than rounded, because the foot itself is exact — 1 ft = 0.3048 m — so 1 ft³ = 0.3048³ = 0.028316846592 m³, about 28.32 litres.
Cubic feet are the working unit on a job site because they come straight out of feet-and-inches measurements with no intermediate conversion. Suppliers, however, quote bulk material by the cubic yard, which is why every result above is shown in both.
What is a cubic yard?
A cubic yard is a cube one yard (3 ft) on each edge: 3 × 3 × 3 = 27 cubic feet, or 36 in × 36 in × 36 in = 46,656 cubic inches. In metric, 1 yd³ = 0.9144³ = 0.764554857984 m³ — and that agrees with 27 × 0.028316846592 = 0.764554857984. Two routes, one number.
Physically it is a pile 3 ft high, 3 ft wide and 3 ft deep — roughly the load of a full-size pickup truck bed heaped, which is why "a yard of mulch" is the natural retail unit and cubic feet are the natural measuring unit.
Densities used for the tons figure
Tonnage is the only part of this page that is not pure arithmetic. These are the loose (delivered) densities the presets apply, with the document each one comes from:
| Material | Loose density (lb/ft³) | Per cubic yard | Source row |
|---|---|---|---|
| Crushed stone / gravel | 100 | 2,700 lb = 1.35 tons | EPA: "Stone, crushed — 1 cubic foot — 100"; corroborated by "Gravel, dry — 1 cubic foot — 100" and "Stone, crushed, size reduced — 1 cubic yard — 2,700" |
| Normal-weight concrete (hardened) | 150 | 4,050 lb = 2.025 tons | PCA EB001: 2,200–2,400 kg/m³ (140–150 lb/ft³) Ch. 6; (137–150 lb/ft³) Ch. 9; glossary "approximately 2400 kg/m3 (150 lb/ft3)" |
| Topsoil | 95 | 2,565 lb = 1.28 tons | Interpolated inside EPA's loose-soil rows: "Soil/sandy loam, loose — 1 cubic yard — 2,392" = 88.6 lb/ft³ and "Earth, wet, containing clay — 1 cubic foot — 100-110". No EPA row prints 95. |
| Wood-chip / shredded mulch | 16.3 | 440 lb = 0.22 tons | EPA: "Wood chips, shredded — 1 cubic yard — 440"; 440 ÷ 27 = 16.296 lb/ft³ |
Why the mulch figure changed. An earlier version of this page used 25 lb/ft³ (675 lb/yd³) for mulch. We could not find that figure in any government or university document we were able to retrieve, so we replaced it with the EPA row rather than keep an unsourced number. Every fetchable authoritative value for loose wood chips is lower: EPA 440 lb/yd³ = 16.3 lb/ft³; a Colorado county biomass report gives fresh green chips around 500 lb/yd³ (18.5 lb/ft³) and dry chips 250–350 lb/yd³ (9.3–13.0 lb/ft³). If your supplier prints a weight per yard on the delivery ticket, use that number instead of any of these — it overrides the table, because it is a measurement of the material you actually bought.
Loose, wet, and compacted
The same material does not weigh the same in every state, and EPA's own table shows it side by side:
| EPA row | Volume | Weight |
|---|---|---|
| Sand, dry | 1 cubic foot | 90–110 lb |
| Sand, moist | 1 cubic foot | 100–110 lb |
| Sand, wet | 1 cubic foot | 110–130 lb |
| Gravel, dry | 1 cubic foot | 100 lb |
| Gravel, wet | 1 cubic foot | 100–120 lb |
| Earth, loose | 1 cubic foot | 76 lb |
| Earth, moist, loose | 1 cubic foot | 78 lb |
| Earth, wet, containing clay | 1 cubic foot | 100–110 lb |
Read the spread: sand at the wet end can weigh 130 ÷ 90 = 1.44× what it weighs at the dry end, and loose earth at 76 lb/ft³ versus wet clayey earth at 110 lb/ft³ is a 1.45× difference for material from the same hole. Moisture alone is a bigger effect than most people expect.
Two consequences. First, every tonnage on this page is a delivered loose volume figure, which is the right basis for ordering — that is what the truck carries. Second, material compacts in place, so a yard of gravel spread and rolled occupies less depth than it did in the pile. We do not print a compaction factor here, because we could not verify one in a retrievable primary document; ask the supplier for the in-place unit weight if the finished depth is critical.
Bags or bulk?
Bagged product is sold by cubic feet, bulk by cubic yard. One cubic yard is 27 ft³, so the bag count is 27 ÷ bag size — and each bag covers bag volume ÷ depth in feet:
| Bag size | Bags per yd³ | Sq ft one bag covers at 3 in | Sq ft one bag covers at 2 in |
|---|---|---|---|
| 1 ft³ | 27 | 4 | 6 |
| 2 ft³ | 13.5 | 8 | 12 |
| 3 ft³ | 9 | 12 | 18 |
Check the middle row against the coverage table: 13.5 bags × 8 sq ft = 108 sq ft, which is exactly what one cubic yard covers at 3 inches. Bag sizes vary by brand — read the label rather than assuming 2 ft³.
Typical depths by material
| Material | Typical depth | 100 sq ft needs | Weight of that volume |
|---|---|---|---|
| Mulch (garden beds) | 2–3 in | 16.67–25 ft³ (0.62–0.93 yd³) | 0.14–0.20 tons at 16.3 lb/ft³ |
| Topsoil (lawns) | 4–6 in | 33.33–50 ft³ (1.23–1.85 yd³) | 1.58–2.38 tons at 95 lb/ft³ |
| Concrete (slab) | 4 in | 33.33 ft³ (1.23 yd³) | 2.50 tons at 150 lb/ft³ |
| Crushed stone (path or base) | 4–6 in | 33.33–50 ft³ (1.23–1.85 yd³) | 1.67–2.50 tons at 100 lb/ft³ |
| Sand (paver bedding) | 1 in | 8.33 ft³ (0.31 yd³) | 0.38–0.46 tons at EPA's 90–110 lb/ft³ dry range |
Mulch depth is the one with a published recommendation behind it: Iowa State University Extension says "Generally, 2 to 4 inches is effective, with coarser mulches (like wood chips) on the higher end and finer mulches (like grass clippings) on the lower end," and that shredded bark mulch "is best at 2 to 3 inches thick," with the further caution to "keep mulch no more than 4" deep and feather it away from the trunks of woody plants." The other depths in this table are common construction practice, not a cited standard.
Reverse: a delivered load back to area
| What you know | Working | Answer |
|---|---|---|
| 10 yd³ of concrete, 4 in slab | 10 × 81 sq ft per yd³ | covers 810 sq ft |
| 5 yd³ of gravel on a 300 sq ft drive | 5 × 27 ÷ 300 = 0.45 ft × 12 | 5.4 in deep |
| 1 yd³ of mulch at 3 in | 324 ÷ 3 | covers 108 sq ft |
| 2 tons of crushed stone at 6 in | 2 × 2,000 ÷ 100 = 40 ft³; 40 ÷ 0.5 | 40 ft³, covering 80 sq ft |
The last row is the one that catches people out: 2 tons sounds like a lot of gravel, and at 6 inches it covers 80 sq ft — an 8 ft × 10 ft patch.
FAQ
How do I convert square feet to cubic feet?
Multiply the area in square feet by the depth in feet. Since depth is normally given in inches, use cubic feet = square feet × (inches ÷ 12). A 100 sq ft bed at 3 inches deep is 100 × 0.25 = 25 cubic feet. There is no conversion without a depth: square feet measure a surface, cubic feet measure what fills it.
How many cubic yards is 100 sq ft at 3 inches deep?
25 cubic feet, and 25 ÷ 27 = 0.9259 cubic yards. Since material is sold by the whole or half yard, order 1 yard. Rounding to the nearest yard gives the same answer here, but at 0.45 yd³ it would round to zero — always round up.
How many tons is one cubic yard of gravel, concrete, or mulch?
Tons = cubic feet × density ÷ 2,000, so one cubic yard (27 cu ft) at the densities this calculator uses is: crushed stone or gravel at 100 lb/ft³ = 2,700 lb = 1.35 tons; normal-weight concrete at 150 lb/ft³ = 4,050 lb = 2.025 tons; topsoil at 95 lb/ft³ = 2,565 lb = 1.28 tons; shredded wood-chip mulch at 16.3 lb/ft³ = 440 lb = 0.22 tons.
What depth should I use for mulch, topsoil, concrete and gravel?
Iowa State University Extension recommends 2 to 4 inches of mulch generally, and 2 to 3 inches specifically for shredded bark mulch, with no more than 4 inches anywhere and mulch feathered away from trunks. Common practice for the rest: topsoil 4–6 inches, concrete slabs 4 inches, gravel paths and paver bases 4–6 inches, and sand bedding about 1 inch.
Why does the mulch preset use 16.3 lb per cubic foot?
Because that is the value we can source. The US EPA volume-to-weight table lists "Wood chips, shredded" as 440 lb per cubic yard, and 440 ÷ 27 = 16.296 lb/ft³. The widely repeated figure of about 25 lb/ft³ (675 lb/yd³) could not be found in any government or university document we were able to retrieve, so we do not use it. Moisture moves the answer a long way: a Colorado county biomass report puts dry chips at 250–350 lb/yd³ (9.3–13.0 lb/ft³) and fresh green chips around 500 lb/yd³ (18.5 lb/ft³).
Should I round cubic yards up or to the nearest yard?
Up. A short load leaves a thin patch you cannot fill with the leftover half yard, and ready-mix concrete is ordered in quarter-yard increments. A 400 sq ft slab at 4 inches is 4.94 yd³ before waste; with 5 percent for spill and subgrade that is 5.19 yd³, so order 5.25. Rounding to the nearest yard would give 5.00 and leave you short.
Sources and How to Check This Page
- Densities for gravel, sand and soil — "Stone, crushed | 1 cubic foot | 100", "Gravel, dry | 1 cubic foot | 100", "Gravel, wet | 1 cubic foot | 100-120", "Stone, crushed, size reduced | 1 cubic yard | 2,700", "Gravel, loose | 1 cubic yard | 2,565", "Sand, dry | 1 cubic foot | 90-110", "Sand, moist | 1 cubic foot | 100-110", "Sand, wet | 1 cubic foot | 110-130", "Soil/sandy loam, loose | 1 cubic yard | 2,392", "Earth, loose | 1 cubic foot | 76", "Earth, moist, loose | 1 cubic foot | 78", "Earth, wet, containing clay | 1 cubic foot | 100-110", and "Wood chips, shredded | 1 cubic yard | 440" — are transcribed from US EPA, Standard Volume-to-Weight Conversion Factors. The underlying rows are attributed in that table to FEECO, Tellus and U.S. EPA. The EPA table is compiled for solid-waste estimation, so treat each figure as a loose-state estimate rather than a specification for a particular supplier's product.
- Concrete density — Design and Control of Concrete Mixtures, EB001, 15th edition, Portland Cement Association: freshly mixed normal-weight concrete "2200 kg/m3 to 2400 kg/m3 (140 lb/ft3 to 150 lb/ft3)" (Ch. 6); conventional concrete "in the range of 2200 kg/m3 to 2400 kg/m3 (137 lb/ft3 to 150 lb/ft3)" (Ch. 9); glossary, normal weight concrete "having a density of approximately 2400 kg/m3 (150 lb/ft3)". Quoted from a full-text copy of the 15th edition at secement.org/wp-content/uploads/2019-01/eb001.15.pdf; the publisher's own product page is cement.org. This is the density of hardened concrete, which is the correct basis for slab volume-to-weight arithmetic.
- Mulch depth — "Generally, 2 to 4 inches is effective, with coarser mulches (like wood chips) on the higher end and finer mulches (like grass clippings) on the lower end"; "This shredded bark mulch is best at 2 to 3 inches thick"; "keep mulch no more than 4" deep and feather it away from the trunks of woody plants" — Iowa State University Extension and Outreach, Using Mulch in the Garden, retrieved 2026-09-25.
- Unit factors — 1 ft = 0.3048 m exactly is the definition in force since 1959 and reaffirmed by 85 FR 62698, FR Doc. 2020-21902; area and volume factors are tabulated in NIST Special Publication 811, Appendix B.9.
- Everything else here is arithmetic on those figures and can be re-derived: 12³ = 1,728 and 36³ = 46,656; 3³ = 27; 0.3048³ = 0.028316846592 m³ and × 27 = 0.764554857984 = 0.9144³; sq ft per yd³ = 324 ÷ depth in inches, giving 324, 162, 108, 81, 64.8, 54, 40.5, 27; 400 ÷ 3 = 133.33 ft³ and ÷ 27 = 4.9383 yd³, × 1.05 = 5.185; 133.33 × 150 ÷ 2,000 = 10.0 tons; 120 ÷ 3 = 40 ft³ = 1.4815 yd³ and × 100 ÷ 2,000 = 2.0 tons; 440 ÷ 27 = 16.296; 100 × 27 = 2,700 lb = 1.35 tons; 150 × 27 = 4,050 lb = 2.025 tons; 95 × 27 = 2,565 lb = 1.2825 tons; 2,392 ÷ 27 = 88.6; 250 ÷ 27 = 9.259, 350 ÷ 27 = 12.963, 500 ÷ 27 = 18.519; 130 ÷ 90 = 1.44 and 110 ÷ 76 = 1.45; 5 × 27 ÷ 300 × 12 = 5.4 in; 2 × 2,000 ÷ 100 = 40 ft³ and ÷ 0.5 = 80 sq ft.
- What we could not source, and therefore do not assert. The often-quoted mulch density of 25 lb/ft³ (NO_SOURCE — every retrievable government or university figure for loose wood chips is 9.3–18.5 lb/ft³); a numeric compaction factor for aggregate in place; typical depths for concrete, topsoil, gravel and sand, which are stated above as common practice rather than as a cited standard; and any material price. A Colorado county biomass report corroborating 250–500 lb/yd³ for chipped wood was read during this audit, but we did not record a retrievable URL for it, so it is mentioned as corroboration only and no figure on this page depends on it.