๐ฑ Fertilizer NPK Nutrient Calculator
Enter the "N-P-K" numbers printed on the fertilizer bag (e.g. 8-8-8).
Calculate the actual amount (g) of each nutrient contained in a bag of fertilizer, from its total weight and its N-P-K (Nitrogen-Phosphorus-Potassium) percentage label. A label like "8-8-8" shows the percentage of nitrogen, phosphorus, and potassium respectively.
How to use
- Enter the fertilizer bag's total weight (g).
- Enter the Nitrogen (N), Phosphorus (P), and Potassium (K) percentages.
- The actual amount (g) of each nutrient is calculated automatically.
How the calculation works
From the numbers on a fertiliser bag, such as โ8-8-8โ, and the amount of fertiliser, calculate the grams of nitrogen, phosphate and potash it contains. Amount of each (g) = fertiliser weight (g) ร percentage รท 100 The numbers are, in order, nitrogen (N), phosphate (PโOโ ) and potash (KโO). By convention, phosphate and potash are given as the weight of their oxides, not of the elements phosphorus and potassium. Nitrogen is said to help leaves and stems, phosphate flowers and fruit, and potash roots, so choose the ratio to suit what you are growing.
Worked example
500 g of an 8-8-8 fertiliser Nitrogen 40 g, phosphate 40 g, potash 40 g To give 20 g of nitrogen with a 10-5-5 fertiliser 20 รท 0.10 = 200 g of fertiliser As elements, about 44% of phosphate (PโOโ ) is phosphorus (P) and about 83% of potash (KโO) is potassium (K).
Things to be aware of
- Too much fertiliser can burn roots. Follow the amounts and intervals on the bag.
- Organic fertilisers tend to act slowly, chemical fertilisers quickly.
- Only the three main nutrients are calculated; calcium, magnesium and other elements are not included.
FAQ
What does a label like "8-8-8" mean?
It shows the percentage by weight of Nitrogen (N), Phosphorus (as P2O5), and Potassium (as K2O), in that order โ a standard labeling format found on every fertilizer bag.
How is the nutrient amount calculated?
Nutrient amount (g) = total fertilizer weight (g) ร percentage (%) รท 100. For example, 1000g of fertilizer with 10% nitrogen contains 100g of nitrogen.
Can this calculate nutrients other than N-P-K?
This tool covers the three primary nutrients shown on standard fertilizer labels โ Nitrogen, Phosphorus, and Potassium. It does not cover secondary or micronutrients.