Use this guide to check the assumptions, then open the gravel calculator with your own figures.
Split the shape
The calculator uses length and width, so irregular spaces are easiest to handle by splitting them into rectangles or estimating an average width.
- Measure each rectangle separately.
- Add the areas together before calculating depth.
- For curves, use an average width and add a sensible allowance.
Record your assumptions
A clear note of the measurements helps when comparing supplier quotes or checking the result later.
- Write down each section's length and width.
- Mark the intended depth.
- Note any areas excluded by steps, drains, planters, or borders.
Weed membrane, edging, and gravel loss
Measure after edging plans are clear and allow for losses around borders and irregular shapes.
Edging changes the finished area
The calculator should use the area that will actually be covered with gravel. If edging, sleepers, kerbs, planters, drains, or stepping stones reduce the finished surface, measure after those decisions are made. That avoids ordering for an area that will not receive gravel.
- Exclude fixed features that will not be covered.
- Measure inside the edging line rather than the rough excavation line.
- Split complex areas into sections and add the results.
Membrane is not a substitute for depth
A membrane may help separate the gravel from soil, but it does not remove the need for a consistent gravel layer. Shallow gravel can still look patchy, expose fabric, or move away from edges. Use the calculator result as a quantity estimate, then check the product and site conditions.
- Choose a depth that hides the base consistently.
- Add an allowance for cuts, corners, and small spills.
- Keep spare material for topping up after the gravel settles.
Preparation checks
The preparation checks reference keeps the relevant comparisons together so each assumption can be checked before changing the calculator inputs.
- Check: Edging line; Why it affects quantity: Defines the finished area; Action: Measure inside the edge.
- Check: Membrane visibility; Why it affects quantity: Can show through shallow gravel; Action: Test a realistic depth.
- Check: Uneven ground; Why it affects quantity: Creates low spots; Action: Use average depth or add allowance.
Irregular measuring methods
| Shape | Simple method | Caution |
|---|---|---|
| L-shaped area | Split into two rectangles | Do not count the overlap twice. |
| Curved border | Use average width | Add allowance for uncertainty. |
| Mixed patio gaps | Measure each gravel section | Exclude paving stones or fixed features. |