General Rule of Thumb for Calculating Polygon Area
For regular polygons—where all sides and angles are equal—a reliable rule of thumb is to use the following formula:
Area = (1/4) × n × s² × cot(π/n)
In this formula, n is the number of sides, s is the length of one side, and cot(π/n) is the cotangent of the angle in radians. This equation gives you the exact area of the polygon’s surface. Once you have the area, simply multiply it by the desired gravel depth to estimate the total volume. Our calculator uses this formula behind the scenes to deliver instant, accurate results for any regular polygon shape.
What If the Polygon Sides Are Not Equal?
If your shed foundation has sides of different lengths or angles, it’s considered an irregular polygon. In these cases, the regular polygon formula doesn't apply. Instead, the most effective way to calculate the area is by dividing the shape into multiple non-overlapping triangles. You can then calculate the area of each triangle individually using our triangle gravel calculator and add up the calculated gravel for all the triangles to come up with the area of your irregular shape polygon.
This approach is common in architectural layout plans and surveying. While it requires more input and planning, it allows for precise estimates when working with custom shed footprints or unconventional garden layouts.
Why Use a Shape-Based Gravel Calculator?
Not every shed project follows the classic square or rectangular footprint. Many modern sheds, especially those used for garden aesthetics, corner placement, or tight spaces, come in alternative shapes like triangles, hexagons, or essentially any polygon. This shape-based gravel calculator is designed specifically for such variations.
Instead of manually estimating the base area and guessing the volume of gravel required, this tool uses shape-specific geometry to give you accurate results.
How to Use This Gravel Shed Foundation Calculator
Begin by identifying the layout of your shed foundation. Select the matching shape from the list of available calculators. If you have a regular polygon, only a single side length is needed. Enter this measurement, along with the desired gravel depth, and choose your preferred unit of measurement.
If you want to fine-tune the result based on the type of gravel, there’s an optional field for density input. If left blank, the calculator uses a balanced default value suitable for general-purpose crushed stone used in shed foundations.
Once you’ve entered the necessary values, the calculator outputs two key results: gravel volume and gravel weight. These are automatically converted into multiple units so you can easily compare, order, and transport the right amount of material.
What Is a Gravel Shed Foundation and Why Use One?
A gravel shed foundation is a compacted stone base laid beneath a shed to provide stable, moisture-resistant support. It’s an increasingly popular alternative to concrete or pavers for its simplicity, cost-efficiency, and drainage benefits.
Unlike solid concrete, a gravel foundation allows water to filter through, reducing the risk of rot and mold under wooden floors. It’s also far easier to construct with basic tools, making it a practical choice for DIY enthusiasts. Moreover, gravel is forgiving on uneven terrain and can be expanded or relocated with minimal effort.
Gravel Density Chart for Shed Foundations
| Gravel Type | Typical Density (kg/m³) | Best Used For |
|---|---|---|
| Crushed Stone (3/4") | 1600–1700 | Reliable base for most sheds |
| Pea Gravel | 1500–1600 | Decorative finishes; light loads |
| Crusher Run / Quarry Dust | 2000–2200 | Heavy equipment or machinery |
| Road Base Mix | 1800–2000 | Sloped or large shed areas |
| River Rock (rounded) | 1400–1500 | Avoid (poor compaction properties) |
Most Common Shed Shapes and Their Applications
- Square or Rectangle: Standard for utility and storage sheds; easy to align with fences or lot lines.
- Hexagon or Octagon: Chosen for decorative sheds, gazebos, or garden spaces with symmetry
- Triangle: Best for tight corners or unconventional layouts where space is limited
- Heptagon: Rare but suitable for artistic or eco-style shed designs
Matching your foundation to the actual shed shape ensures you calculate gravel requirements with precision and avoid overbuying.
How Deep Should the Gravel Base Be?
A typical shed base needs 4 to 6 inches of gravel. Heavier structures may require up to 8 inches. Always compact in layers (2 to 3 inches at a time) for a stronger, more stable foundation.
It's smart to plan for 5–10% more gravel than calculated. That margin accounts for compaction, leveling irregularities, and unplanned adjustments during installation.
What Kind of Gravel Should NOT Be Used as Shed Foundation?
- River rock – Smooth and round, it doesn’t lock together when compacted
- Sand or soil mixes – Retain moisture and shift under load
- Decorative gravel – Lacks the structural integrity for load-bearing use
- Any loose material that does not compact – Unstable under pressure
Always use angular, compactable materials like crushed stone or crusher run for strong, durable shed bases.
FAQs: Shed Gravel Foundations
Can I place pavers or concrete blocks over this gravel base?
Yes. A compacted gravel base supports pavers, blocks, or wood skids effectively.
How do I prepare the ground before laying gravel?
Clear vegetation, remove topsoil, level the surface, compact the subsoil, and lay landscape fabric if needed.
Do I need edging for shaped foundations like hexagons or triangles?
Yes. Edging helps hold gravel in place and prevents the shape from deforming over time, especially for curved or polygonal layouts.
How much extra gravel should I order?
Always plan for 5–10% more gravel than the calculated amount. This accounts for compaction, shaping losses, and depth fluctuations during installation.