Convert P₂O₅ to P

Converting P₂O₅ to P

When you see fertilizer labels or soil test reports, phosphorus content is often given as P₂O₅ (phosphorus pentoxide).
However, the actual amount of elemental phosphorus (P) in that compound is less because P₂O₅ contains oxygen as well.
To know how much elemental phosphorus (P) you have or apply, you need to convert P₂O₅ to P.

How to Convert P₂O₅ to P

Molecular weight of P₂O₅ = 2 × atomic weight of P + 5 × atomic weight of O
= 2 × 31 + 5 × 16
= 62 + 80
= 142 g/mol
Molecular weight of elemental phosphorus (P) in P₂O₅ = 2 × 31 = 62 g/mol
So, the fraction of P in P₂O₅ is:
$62142\approx0.436$
This means 1 kg of P₂O₅ contains approximately 0.436 kg of elemental P.

Calculator Formula

To convert a given amount of P₂O₅ to P:

$P (kg)=P₂O₅ (kg)\times0.436$

Example:

If your fertilizer has 50 kg of P₂O₅, the amount of elemental phosphorus (P) is:

$50\times0.436=21.8 kg of P$

You can find more agriculture conversion calculators here.

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