Estimate a uniform rectangular gravel-fill zone for a shed pad. The example 12 × 10-foot shed with 1 foot added on every side gives a 14 × 12-foot pad. At 4 inches deep with a selected 10% allowance, the model returns 2.28 cubic yards. This is geometry with an allowance, not a foundation design or an automatic loose-delivery order.
Shed-pad quantity formulas
Pad length = shed length + 2 × extension.
Pad width = shed width + 2 × extension.
Net cubic yards = pad area × depth in inches / 324.
Adjusted volume = net volume × (1 + allowance / 100).
US short tons = adjusted cubic yards × supplier short tons per cubic yard. These are our quantity formulas. They assume the whole rectangle is gravel fill at one depth.
Choose the base detail before ordering
Site Prep, a shed-foundation contractor, recommends a 12-inch extension on each side and gives a general 4–6-inch depth range for its gravel foundations.1 Those are that contractor’s recommendations, not specifications for every shed. Confirm the shed maker’s support, material, anchoring and base requirements and the local rules for your site.
If a perimeter frame occupies part of the pad outline, use the actual inside gravel-fill dimensions. This form does not subtract lumber or model varying depth on a sloping site. Calculate separate non-overlapping fill zones when one uniform rectangle does not describe the work.
Keep finished geometry, loose order volume, handling reserve and supplier density separate. The allowance field does not establish a compaction conversion. Ask the supplier for a defined relationship if your measured finished layer and delivered loose material have different volume bases. See gravel quantities by shed size and shed-base material selection.
Net gravel chart: selected 1-foot extension
Our calculated table uses a 1-foot extension on every side. Depths are comparison inputs, not construction instructions. Values exclude allowances and any loose-to-compacted conversion.
| Shed (ft) | Fill pad (ft) | Area (sq ft) | 4-in layer (yd³) | 6-in layer (yd³) |
|---|---|---|---|---|
| 8 × 8 | 10 × 10 | 100 | 1.235 | 1.852 |
| 10 × 12 | 12 × 14 | 168 | 2.074 | 3.111 |
| 12 × 16 | 14 × 18 | 252 | 3.111 | 4.667 |
| 12 × 20 | 14 × 22 | 308 | 3.802 | 5.704 |
Three checked examples
1. Default US quantity model
A 12 × 10-foot shed plus 1 foot on each side gives 14 × 12 = 168 sq ft. At 4 inches: 168 × 4 / 12 = 56 cu ft = 2.074074 yd³. A selected 10% allowance gives 61.6 cu ft = 2.281481 yd³. At the example 1.4 short tons/yd³, that is 3.194074 short tons. The density is an input, not a verified value for your stone.
2. No extension or allowance
A 12 × 10-foot fill rectangle at 4 inches gives 120 × 4 / 12 = 40 cu ft = 1.481481 yd³. Zero extension and zero allowance are valid arithmetic inputs, not approval of that base layout. At an example 1.4 short tons/yd³, the result is 2.074074 short tons.
3. Independently entered metric dimensions
A 4 × 3-meter shed with 0.5 meter on every side gives a 5 × 4-meter fill rectangle. At 10 cm deep: 20 × 0.10 = 2.00 m³. A selected 10% allowance gives 2.20 m³. At an example supplier density of 1.5 tonne/m³, the result is 3.30 metric tonnes. Product, volume basis and supplier order increments still need checking.
Does 10% extra account for compaction?
Not by itself. It is a selected allowance. Only a defined material-specific relationship can convert a finished layer volume to a loose delivered volume. Do not add a second allowance if your supplier has already included it.
Is the displayed tonnage a safe truck load?
No. It is a density-based material estimate, not a vehicle payload check. Verify the actual load and vehicle limits separately.
Can the calculator choose the foundation?
No. It does not check soil bearing, frost requirements, drainage, anchoring or shed loads. Resolve the required base detail first.
Sources
- Site Prep: shed foundation FAQs (contractor guidance on extension, depth, material and local checks)
What you’ll need
A plain checklist. Needs vary by project, so follow the instructions on your materials.
- Specified separation or stabilization material – follow the base design; a weed-barrier listing alone does not establish suitability.
- Timber or paver border – holds the pad edges.
- Compactor and rake – for a firm level base.
- Level and string line – a shed floor should sit flat.
- Gravel – see the gravel calculator.
Popular tools: Concrete | Gravel | Mulch | Paint | Tile | Flooring | Topsoil | Sod | Roofing | Drywall | All calculators
Guide: How much gravel for a shed base (tons by shed size)
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Estimates only. Confirm quantities and product details with your supplier or installer before you order. This is not professional advice.