Convert P to P₂O₅

P to P₂O₅ Conversion

Phosphorus (P) is the element measured in soil or fertilizer.
Phosphorus pentoxide (P₂O₅) is how phosphorus content is usually expressed in fertilizers.
To compare or calculate fertilizer needs, you often need to convert between these two.

Why convert?
Fertilizer labels usually show nutrient content as oxides (like P₂O₅), but soil tests report the element itself (P). So, you convert to know how much fertilizer you need.

How to Convert

Molecular weight of P = 31 g/mol
Molecular weight of P₂O₅ = 2×31 + 5×16 = 62 + 80 = 142 g/mol

Since P₂O₅ contains 2 atoms of P:

Weight of P in P₂O₅ = 62 g
Weight ratio: $14262\approx2.29$

Conversion Formulas

To convert P to P₂O₅:
$P₂O₅ =P\times2.29$
To convert P₂O₅ to P:
$P= P₂O₅/ 2.29$

Calculator Example

If soil test shows 20 kg/ha P, then:

$P₂O₅ =20\times2.29=45.8 kg/ha$

You need fertilizer containing about 45.8 kg/ha of P₂O₅ to supply that amount of phosphorus.

You can find more agriculture conversion calculators here.

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