NPK from Fertilizer Grade & What's Really in the Bag

The grade is the three numbers on the bag — like 19-19-19 or 10-26-26 — giving the percentage by weight of nitrogen (N), phosphorus as P₂O₅ and potassium as K₂O, in that order. A 19-19-19 bag is 19% each of N, P₂O₅ and K₂O; the remaining 43% is filler, secondary nutrients or other carriers.

Nutrient kg = product weight × grade% ÷ 100. A 50 kg bag of 19-19-19 supplies 50 × 0.19 = 9.5 kg each of N, P₂O₅ and K₂O — about 28.5 kg of total nutrient and roughly 21.5 kg of other material. The tool does this for each of the three numbers and adds them up.

Because grades report only the three primary nutrients. The rest of the bag is filler, the carrier compound, water of crystallisation, or secondary and micronutrients like sulphur and zinc. A 19-19-19 (57% nutrient) bag therefore has about 43% other material — that's normal and varies between products.

Fertilizer phosphorus and potassium are quoted as oxides by convention: P₂O₅ (phosphate) and K₂O (potash), not as elemental P and K. So the grade's middle and last numbers are oxide percentages. If you need elemental amounts, multiply P₂O₅ by 0.44 for P and K₂O by 0.83 for K.

Work out your crop's recommended N-P-K dose per acre, then use this tool to see how much of each nutrient a bag of your fertilizer supplies. Divide the dose by the nutrient per bag to find how many bags you need — or combine fertilizers to hit all three targets. The Fertilizer (NPK) Calculator handles the full dose-to-bags step.

The grade is the actual percentages (19-19-19), while the ratio is those numbers simplified (1-1-1). Two fertilizers can share a ratio but differ in grade and concentration — a 10-10-10 and a 19-19-19 are both 1-1-1 but the 19-19-19 packs nearly twice the nutrient per kg, so you use less of it.

Yes — enter the grade of any straight or complex fertilizer (urea 46-0-0, DAP 18-46-0, MOP 0-0-60, 12-32-16, 19-19-19 and so on) with the product weight, and it returns the kg of N, P₂O₅ and K₂O plus the total nutrient. Any grade and any bag size or unit works.

Total nutrient (N + P₂O₅ + K₂O) tells you how concentrated a fertilizer is and helps compare value between products — more total nutrient per kg often means lower cost per unit of nutrient and less material to handle and apply. Use it alongside the Fertilizer Cost per Nutrient tool to compare prices fairly.

The nutrient amounts are exact arithmetic from the grade you enter, so they're as accurate as the grade printed on the bag. What varies in the field is how much of that nutrient the crop actually takes up, which depends on soil, moisture, timing and method — so match the dose and apply well to realise the supply.

Yes — calculate the nutrients each fertilizer supplies, then add them to see the combined N, P₂O₅ and K₂O of a blend and check it against your crop's target. For designing a custom blend to a target grade, the Fertilizer Blend Grade Calculator is the dedicated tool.