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Soil Calculators

Soil Test ppm to kg/ha Calculator

Convert a soil test result from ppm (mg/kg) to kg per hectare and kg per acre, using sampling depth and bulk density.

Enter your details

The concentration from your soil report.

ppm (mg/kg)

Usually 0–15 cm for field crops.

About 1.3–1.6 for most mineral soils. Use 1.5 if unknown.

g/cm³

Please note: This calculator provides a mathematical estimate based on the values entered. Recommended agricultural application rates can vary by crop, soil, product formulation, location and official agricultural guidance. Check the product label and local agricultural recommendations before application.

Your soil report says "12 ppm phosphorus" – but fertilizer is planned in kg per hectare. Enter the ppm value, how deep the sample was taken and the soil's bulk density, and get the nutrient in kg per hectare and per acre.

About the Soil Test ppm to kg/ha Calculator

ppm (parts per million) means milligrams of nutrient per kilogram of soil. It's a concentration. kg/ha is an amount spread over an area. To convert one to the other you need to know how much soil you're talking about – and that depends on how deep the sample was taken and how dense the soil is.

For the standard plough-layer sample (0–15 cm) and a typical bulk density of 1.5 g/cm³, one hectare of that layer weighs about 2,250 tonnes. That gives the well-known rule of thumb:

kg/ha ≈ ppm × 2.25 (for 15 cm depth and bulk density 1.5)

You'll also see "ppm × 2" used as a quick approximation – it assumes a lighter soil or a slightly shallower layer. This calculator lets you enter your actual depth and bulk density instead of relying on either shortcut.

Next step

Soil reports often give phosphorus and potassium as the elements P and K. Fertilizer recommendations use P2O5 and K2O. Once you have kg/ha, convert with the P to P2O5 and K to K2O converter.

How to use the Soil Test ppm to kg/ha Calculator

  1. 1 Enter the nutrient value from your soil report in ppm (or mg/kg – they are the same).
  2. 2 Enter the depth the sample was taken to – usually 15 cm.
  3. 3 Enter the bulk density if you know it; otherwise leave 1.5.
  4. 4 Press Convert.

The formula we use

Soil mass (t/ha) = 10,000 m² × Depth (m) × Bulk density (t/m³)
kg/ha = ppm × Depth (cm) × Bulk density (g/cm³) × 0.1
kg/acre = kg/ha ÷ 2.471

At 15 cm and 1.5 g/cm³: 15 × 1.5 × 0.1 = 2.25.

Worked example

A soil report shows 12 ppm available phosphorus (Olsen P) in a 0–15 cm sample; bulk density assumed 1.5 g/cm³.

  1. Factor = 15 × 1.5 × 0.1 = 2.25.
  2. P = 12 × 2.25 = 27 kg/ha (10.9 kg per acre) of elemental P.
  3. As P2O5: 27 × 2.29 = 61.9 kg/ha.

Things to keep in mind

  • Available vs total. Soil tests measure the "available" fraction extracted by a particular method (e.g. Olsen or Bray for P). Rating tables for low, medium and high are specific to that method.
  • Interpretation. Your soil testing laboratory or Soil Health Card gives ratings and recommendations; this converter only changes the unit.

Frequently asked questions

How do I convert ppm to kg per hectare?

Multiply ppm by depth (cm) × bulk density (g/cm³) × 0.1. For a 15 cm sample at 1.5 g/cm³, multiply by 2.25.

Is ppm the same as mg/kg?

Yes. 1 ppm in soil means 1 mg of nutrient per kg of soil.

Why do some people multiply ppm by 2?

It is a rough rule that assumes about 2,000 tonnes of soil per hectare in the plough layer. Using your actual depth and bulk density is more accurate.

Guides that use this calculator

Last updated . Spotted a mistake or need a unit we don't support? Tell us.