Shed Foundation Calculator
Estimate preliminary materials for gravel pads, skid foundations, concrete slabs or user-defined support grids.
To estimate a shed foundation, multiply the foundation area by the compacted gravel depth or concrete thickness, convert the result to cubic yards or cubic meters, and add compaction and waste allowances. For block or pier foundations, multiply the user-defined support rows by supports per row and blocks per support. Final foundation design must be confirmed for the shed, soil, frost conditions, loads, drainage, and local requirements.
Foundation Method
Shed and Foundation Dimensions
Foundation dimensions, extensions, setbacks, and construction method must be confirmed for the shed, site, manufacturer, and locally applicable requirements.
Gravel and Excavation
Fabric uses area-only math and does not create a strip-layout or seam plan. Neither fabric nor edging is implied as universally required.
Your Estimate
Selected Foundation Method
Compacted Gravel Pad
Shed Footprint
120.00 sq ft
Foundation Dimensions
14.00 × 12.00 ft
Foundation Area
168.00 sq ft
Compacted Gravel Volume
56.00 cu ft (2.07 cu yd)
Loose Volume Before Waste
64.40 cu ft (2.39 cu yd)
Waste-Adjusted Gravel Order
67.62 cu ft (2.50 cu yd)
Excavated Soil Volume
84.00 cu ft (3.11 cu yd)
Fabric Area Required
184.80 sq ft
Landscape Fabric Rolls
1 rolls
Partial material estimate only. Excludes anything not entered, including labor, excavation, hauling, grading, drainage, engineering, permits, inspections, equipment, anchorage, and taxes.
Results Actions
Material estimate only; foundation method, soil bearing, drainage, frost protection, structural design, support spacing and anchorage require project-specific confirmation.
Shed Foundation Material-Planning Reference
These are estimating categories, not universal depths, slab thicknesses, support spacing, footing sizes or approved layouts.
How to Use the Shed Foundation Calculator
- 1Choose Imperial or Metric units and one of four foundation methods.
- 2Enter shed dimensions and separate front, back, left and right extensions.
- 3For gravel, enter established excavation and compacted depths, compaction and waste.
- 4Optionally enter supplier density and choose volume, weight or no gravel pricing.
- 5Optionally estimate area-based landscape fabric and perimeter stock.
- 6For skid mode, enter the project-confirmed skid count, length and available stock.
- 7For slab mode, enter slab geometry, concrete pricing method and optional fixed allowances.
- 8For grid mode, enter the complete user-defined support grid and optional gravel base.
- 9Review quantities and confirm the complete foundation design before purchasing or building.
Shed Foundation Material Formulas
- 1Pad length = shed length + front + back extensions; pad width = shed width + left + right extensions; area = length × width.
- 2Excavation = pad area × excavation depth. Compacted gravel = applicable area × finished depth.
- 3Loose gravel = compacted volume × (1 + compaction percentage). Final order = loose volume × (1 + waste percentage).
- 4Optional gravel weight = final volume × supplier-entered density. Volume and weight pricing are mutually exclusive.
- 5Fabric required = pad area × (1 + fabric waste); rolls = required area ÷ roll area, rounded up. This is not a seam plan.
- 6Perimeter = 2 × (pad length + pad width); edging pieces round up after waste.
- 7Skid pieces per skid = skid length ÷ stock length, rounded up; purchase pieces add waste after multiplying by entered skid count.
- 8Concrete = slab area × entered thickness; waste is applied once. Bags use published volume yield and round up.
- 9Grid supports = rows × supports per row + extras; blocks = support locations × blocks per support.
- 10Partial budget = enabled priced items + entered contingency.
Imperial Gravel, Metric Slab, and Block-Grid Examples
Every dimension and allowance is a hypothetical user-entered planning value, not a recommendation. Imperial gravel example: a 12 ft × 10 ft shed with 1 ft extensions creates a 14 ft × 12 ft pad, or 168 sq ft. At an entered 4 in compacted depth, compacted volume is 56 cu ft (2.07 cu yd). With 15% compaction allowance and 5% waste, order volume is about 2.50 cu yd. At a supplier-entered 1.4 tons per cu yd, estimated weight is 3.50 tons; a hypothetical $40 per cu yd price would produce $100 gravel cost. Metric slab example: a user enters a 3.5 m × 3 m slab, 10 cm thick, 10% concrete waste and a 10 cm gravel base. Concrete is 1.05 m³ before waste and 1.155 m³ (1,155 L) after waste. At a published 17 L yield, 68 bags are required. Block-grid example: 2 rows × 3 supports plus 1 extra gives 7 support locations; at 2 blocks per support, total is 14 blocks. None of these inputs establishes structural suitability.
Accuracy & Assumptions
- All dimensions, depths, extensions, skid counts and support grids are supplied and approved elsewhere by the user.
- Compaction allowance is applied once to finished compacted gravel and waste is applied once afterward.
- Weight appears only with positive supplier-entered density.
- Fabric uses area-only coverage and does not optimize strips, overlap or seams.
- Skid stock rounds separately per skid and does not approve joints or structural properties.
- Slab calculations use full uniform thickness and do not design reinforcement, joints, edges or foundations.
- Concrete bags use published volume yield, never bag weight.
- Block or pier mode counts a user-defined layout and does not select spacing, bearing or unit type.
- Costs include only enabled and priced items; blank values are omitted.
- Excavated soil volume is in-place geometry and can change after loosening and hauling.
Frequently Asked Questions
How much gravel do I need for a shed foundation?
Multiply confirmed pad area by compacted depth, then apply entered compaction and waste allowances.
How large should a gravel shed pad be?
Use dimensions and extensions confirmed for the shed, drainage, site and local requirements.
How deep should a shed gravel pad be?
Depth is project-specific; the calculator does not select it.
Does the calculator determine the required gravel depth?
No.
What is a compaction allowance?
It converts finished compacted volume into a larger loose ordering volume using an entered percentage.
How is gravel converted to tons or tonnes?
Final volume is multiplied by supplier-confirmed density.
Do I need landscape fabric?
Not universally; follow the approved site and drainage detail.
How much concrete is needed for a shed slab?
Multiply entered slab area by entered thickness and add waste.
Does the calculator determine slab thickness?
No.
How many concrete bags are needed?
Divide waste-adjusted volume by published volume yield and round up.
How many blocks or piers does a shed need?
Enter the approved rows, supports per row, extras and units per support.
Does the calculator determine safe pier spacing?
No.
How many skids does a shed need?
Use the quantity specified for the shed; it is not derived from width.
Can I place a shed directly on gravel?
Only when the selected shed and approved site design permit it.
How do drainage and slope affect the foundation?
They can change grading, pad geometry, erosion control and foundation selection.
Does frost depth matter?
It can materially affect foundation requirements.
Are permits required?
Requirements vary; confirm locally.
Is the estimate a construction or permit-ready plan?
No, it is a preliminary material estimate.
This calculator estimates materials only and does not select or approve a foundation system, soil bearing, drainage, frost protection, slab design, support spacing, anchorage, wind or uplift resistance, or structural capacity. Shed size, weight, floor system, manufacturer instructions, terrain, groundwater, soil, climate and local requirements can change the design. Follow manufacturer requirements, approved plans, permits, setbacks, inspections and locally applicable rules. Locate underground utilities before excavation and properly verify boundaries and setbacks. Consult a qualified installer, manufacturer, professional or local authority where appropriate. No result is structurally approved, code-compliant or permit-ready.