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What do the 3 numbers on a fertilizer bag mean

The three numbers indicate the percentages of nitrogen, phosphorous and potassium
Photo: Wikiphoto
Three numbers on the fertilizer label

The three numbers on a bag of fertilizer indicate the respective percentages of nitrogen (N), phosphorous (P) and potassium (K) it contains. Bags sometimes also show the percentages of calcium (Ca), magnesium (Mg), sulphur (S) and some micronutrients.

For example: Fertilizer marked 15-15-30 contains 15% nitrogen, 15% phosphorous and 30% potassium.

To convert these percentages into kg or lb, just multiply them by the weight of the bag.

For example: A 30-kg bag of 15-15-30 contains:

Nitrogen 15% of 30 kg = 4.5 kg
Phosphorous 15% of 30 kg = 4.5 kg
Potassium 30% of 30 kg = 9 kg
Total 60% of 30 kg = 18 kg

The rest of the bag (12 kg or 40%) may contain secondary elements, micronutrients, impurities and fill.

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