Garden measurement & conversion reference
A UK-focused quick reference for the units that feed garden calculators: length, area, volume, hectares, acres, rainfall and imperial gallons.
Length
| Conversion | Value |
|---|---|
| 1 metre | 100 centimetres |
| 1 metre | 1,000 millimetres |
| 1 metre | 3.28084 feet |
| 1 foot | 0.3048 metres |
Use length for straight runs, hedge lines, edging and sleeper courses. Do not substitute a square-metre area for a linear boundary.
Area
| Conversion | Value |
|---|---|
| 1 m² | 10.7639 ft² |
| 1 hectare | 10,000 m² |
| 1 acre | 4,046.856 m² (approx.) |
| 1 hectare | 2.47105 acres (approx.) |
Area is the starting point for lawns, gravel, paving, topsoil and many planting layouts.
Volume
| Conversion | Value |
|---|---|
| 1 m³ | 1,000 litres |
| 1 litre | 0.001 m³ |
| 1 UK imperial gallon | 4.54609 litres |
| 1,000 litres | 219.969 UK imperial gallons |
Gardeners Toolkit labels UK imperial gallons explicitly. US gallons use a different conversion and should not be mixed into UK pond calculations.
Rainfall and applied water
| Depth over area | Volume |
|---|---|
| 1mm over 1m² | 1 litre |
| 5mm over 10m² | 50 litres |
| 10mm over 100m² | 1,000 litres |
This identity works for both rainfall collection before losses and a selected watering depth. The practical efficiency or horticultural target is a separate input.
Area formulas used across the site
Rectangle
area = length × widthUse the actual surface dimensions. A 5m × 4m rectangle is 20m².
Circle
area = π × radius²If you measure diameter, divide it by two before squaring the radius.
Triangle
area = ½ × base × perpendicular heightThe height is the perpendicular distance to the base, not an arbitrary sloping side.
Ellipse
area = π × semi-major radius × semi-minor radiusUseful for oval pond footprints when the maximum length and width are known.
Area, perimeter and volume are different questions
A 5m × 3m bed has an area of 15m² but a perimeter of 16m. That means a mulch calculation and an edging calculation for the same bed begin with different measurements. Add a 50mm layer and the material volume becomes 15 × 0.05 = 0.75m³, or 750 litres.
Irregular gardens
Do not force an awkward lawn or border into one large rectangle if that includes large areas that are not part of the project. Sketch the space, split it into simple measured zones, subtract known exclusions and use the Garden Area Calculator for the combined total.
Keep measurement precision realistic
A calculator can display many decimal places, but a garden measurement taken with a tape around a curved border is not laboratory data. Keep enough precision to avoid rounding errors, then make purchasing decisions in the whole bags, rolls, slabs or plants that are actually available.
Put the conversions to work
Start with measurement when the project area is uncertain; switch to the depth reference when the job becomes a material layer.