Soil Calculators
Make sense of soil test reports – ppm to kg per hectare, and elemental P and K to P2O5 and K2O.
Reading a soil test report
Soil test reports use different units depending on the lab. Some give available nutrients in kg per hectare, others in ppm (mg per kg of soil). Some report phosphorus as elemental P, others as P2O5. Before you can compare a report with a fertilizer recommendation, everything needs to be in the same units.
- Soil Test ppm to kg/ha Calculator – converts a concentration into the amount of nutrient in the plough layer, using your sampling depth and soil bulk density.
- P to P2O5 and K to K2O Converter – switches between the elemental and oxide forms used on reports and fertilizer bags.
Once your numbers are in kg/ha of P2O5 and K2O, you can use the NPK Calculator to turn the recommended dose into bags of fertilizer.
Frequently asked questions
Why does the ppm to kg/ha factor change?
Because it depends on how much soil you are counting. A deeper sample or a denser soil means more kilograms of soil per hectare, so the same ppm represents more nutrient. For 15 cm depth and bulk density 1.5 g/cm³ the factor is 2.25.