NPK Calculator
Audit fertilizer blends and targets, split NPK ratios, and convert P2O5 to P or K2O to K.
Calculations stay in this browser. If you choose Copy link, the entered blend, target and conversion values are placed in the page URL so the link can reproduce them; that URL can appear in browser history and may be visible to anyone you share it with.
Audits what a fertilizer blend supplies to a whole field and per hectare, compares it with an optional target, splits N:P:K ratios, and converts phosphorus and potassium between oxide and elemental forms.
How to use it
- 1Choose kilograms or bags, enter each fertilizer grade and amount, then set the field size in an Indian or custom land unit.
- 2Read total product, whole-field nutrients and kg/ha; add a target to see each N-P₂O₅-K₂O shortage or excess.
- 3Use the separate ratio split and bidirectional P₂O₅ ↔ P or K₂O ↔ K converters when the recommendation uses a different basis.
Example
- Input
- 100 kg of urea plus 50 kg of DAP, per hectare
- Output
- 55 kg N, 23 kg P₂O₅, 0 kg K₂O — a ratio of 1 : 0.42 : 0
The nitrogen is 55 rather than 46 because the DAP contributes 9 kg on top of the urea's 46. Nothing supplies potassium, so a crop needing K would be short.
What happens to your data
The oxide conversions use the standard factors (P₂O₅ × 0.4364 and K₂O × 0.8302). Everything is arithmetic in the page; nothing is uploaded. A share link contains only the inputs you choose to copy into its query string.
Last updated September 2026
N-P-K is three numbers that look simpler than they are.
The first is nitrogen and means what it says. The other two usually do not: on an Indian or British recommendation, and on almost every fertilizer sack, phosphorus is stated as P₂O₅ and potassium as K₂O — oxides, not elements. Many soil reports give the elements instead. Read a 60 kg elemental-P figure as though it were P₂O₅ and you apply under half the phosphorus intended, while both numbers look ordinary.
Blend mode answers the practical audit: enter each product in kilograms or bags, set the real field area, and see whole-field totals and kg/ha. Add an adviser-supplied target to expose every shortage and excess rather than judging a blend by its label. The other modes split a ratio such as 4:2:1 into kilograms and convert both P₂O₅ ↔ P and K₂O ↔ K.
This audits a mix you supply. It does not optimise the cheapest whole-bag purchase or prescribe a crop dose; the separate fertilizer optimizer handles purchasing after you bring a soil-test or adviser target.
How it works
Toolvore starts with the printed grades of urea, DAP, MOP, SSP and common complexes. Each row accepts kilograms or a number of bags with an editable bag weight. The selected Indian, acre/hectare or custom field unit is converted to hectares; product weight times grade produces N, P₂O₅ and K₂O for the whole field, then division by area produces kg/ha. An optional three-part target is compared with a 0.01 kg tolerance so floating-point dust reads as an exact match while real shortage or excess stays visible.
Ratio mode divides each part by the sum and multiplies by the total. Conversion mode is genuinely bidirectional: the oxide-to-element factors are P₂O₅ × 0.4364 and K₂O × 0.8302, with the inverse used when starting from elemental P or K.
All arithmetic runs locally. The share button puts at most eight product rows and the other current inputs into the page URL, updates the address bar and copies it when the browser permits, so another device can reproduce the same audit. No calculation is uploaded or stored by Toolvore.
Common use cases
- Checking what a mix already planned actually supplies before buying it
- Spotting that a blend supplies no potassium at all for a crop that needs it
- Turning a ratio-style recommendation like 4:2:1 into kilograms per hectare
- Converting a European or soil-report phosphorus figure into the P₂O₅ form an Indian recommendation uses
- Seeing how much nitrogen a phosphorus product is quietly adding to a mix
Frequently asked questions
What do the three numbers on a fertilizer sack mean?＋
Percentages by weight of nitrogen, phosphorus and potassium — but only the first is the element itself. The second is phosphorus expressed as P₂O₅ and the third is potassium expressed as K₂O, which is a convention from the days when these were reported as oxides after burning a sample. So 10-26-26 means 10% nitrogen, 26% P₂O₅ and 26% K₂O by weight. In elemental terms that same sack is about 10% N, 11.3% P and 21.6% K.
Why is my mix supplying more nitrogen than the urea alone?＋
Because a phosphorus product is usually carrying some too. DAP is 18% nitrogen alongside its 46% phosphorus, so 50 kg of DAP quietly adds 9 kg of nitrogen. In the worked example that is why 100 kg of urea and 50 of DAP comes to 55 kg of nitrogen rather than 46. If you sized the urea on the full nitrogen requirement before adding the DAP, you have over-applied by exactly that amount.
How do I convert P₂O₅ to P?＋
Multiply by 0.4364. Going the other way, multiply elemental P by 2.291. For potassium the factors are 0.8302 and 1.205. They come from the molecular weights and never change. The reason it matters: a 60 kg P₂O₅ recommendation and a 60 kg elemental-P recommendation are more than twice apart, and both look like perfectly ordinary doses, so the mistake leaves no trace until the crop shows it.
What ratio should I use?＋
That is not a question this page can answer, and be wary of any that does. The right ratio depends on your soil, the crop, the variety and what grew there last season. Get it from a soil health card, your state agriculture department or your nearest Krishi Vigyan Kendra, then bring it here to turn into numbers.
Why does this not tell me how many bags to buy?＋
Bag mode audits a quantity you enter; it does not round a nutrient target into a purchase plan. Whole-bag purchasing has prices, stock, product choices and unavoidable surplus, which the fertilizer optimizer models separately. Use this page when you already have a proposed mix and want to check what it delivers.
Can I enter a ratio with a zero in it?＋
Yes. 2:1:0 is a perfectly normal recommendation for a field that already tests high in potassium, and the split will simply return zero for K₂O. What it will not accept is all three at zero, since there is nothing to divide.
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