Fertiliser Quantity Calculator
Convert an NPK recommendation into bags of urea, DAP and MOP to buy.
Recommendations come in kilograms of nitrogen, phosphorus and potassium. Shops sell urea, DAP and MOP, each containing different amounts of those nutrients. This calculator converts one into the other — and correctly deducts the nitrogen that DAP already supplies, which is the step most costings miss.
Recommendation and area
Result
Fill in the fields above and your result will appear here.
What the Fertiliser Quantity Calculator does
Urea is 46% nitrogen. DAP is 46% phosphorus and also 18% nitrogen. MOP is 60% potassium. Because DAP carries nitrogen as well as phosphorus, applying the full urea dose on top of a full DAP dose over-applies nitrogen — wasting money and encouraging excessive vegetative growth.
The right order is: meet the phosphorus requirement with DAP, count the nitrogen that provides, and use urea only for the shortfall. That is what this calculator does.
How to use this tool
- Select your crop to load a typical NPK dose per acre, then replace it with the recommendation from your soil health card.
- Enter your plot area in whatever unit you use.
- Check the three nutrient figures — these are kilograms of N, P₂O₅ and K₂O per acre, not kilograms of fertiliser.
- Enter current bag prices from your dealer.
- Buy the whole bags shown. Nitrogen should then be split across a basal dose and one or two top dressings.
Formula and method
Nutrient content: Urea 46% N · DAP 18% N and 46% P · MOP 60% K
DAP needed = Total phosphorus ÷ 0.46
N from DAP = DAP quantity × 0.18
Urea needed = (Total nitrogen − N from DAP) ÷ 0.46
MOP needed = Total potassium ÷ 0.60
Bags: urea 45 kg · DAP 50 kg · MOP 50 kg
Worked example
Example: 5 acres of wheat at 48:24:16 per acre
| Total requirement | 240 kg N, 120 kg P, 80 kg K |
| DAP for phosphorus | 261 kg — about 6 bags |
| Nitrogen from that DAP | 47 kg |
| Urea for the remaining 193 kg N | 420 kg — about 10 bags |
| MOP for potassium | 133 kg — about 3 bags |
Ignoring the nitrogen in DAP would have suggested 12 bags of urea instead of 10 — two bags of unnecessary nitrogen on a five-acre plot, every season.
What your result means
Bags are rounded up, because fertiliser is sold in whole bags. Small excesses store well if kept dry.
Cost per acre feeds directly into the crop profit calculator as one of the largest cash costs of the season.
If no urea is needed, the phosphorus requirement is high enough that DAP alone over-supplies nitrogen. Using SSP for phosphorus instead avoids that.
Important considerations
- A soil health card gives a field-specific recommendation and is far better than any generic dose. Testing costs little and is often subsidised.
- Split nitrogen application. Applying all urea at sowing wastes much of it to leaching and volatilisation; two or three splits with irrigation are standard practice.
- Sulphur, zinc and boron deficiencies are widespread in Indian soils and are not covered by NPK alone. Mustard and pulses in particular respond strongly to sulphur.
- Complex fertilisers such as 10:26:26 and 12:32:16 can be more convenient but make it harder to match a specific NPK ratio.
- Organic manure improves soil structure and supplies micronutrients. Where you apply farmyard manure, the chemical requirement can be reduced.
- Urea bags were reduced from 50 kg to 45 kg for subsidised urea. Check the bag weight before converting.
Limitations of this tool
- It covers nitrogen, phosphorus and potassium only. Secondary nutrients and micronutrients are not modelled.
- It assumes DAP for all phosphorus. SSP, complex fertilisers and organic sources would change the schedule.
- It does not schedule application timing, which matters as much as quantity for nitrogen.
Frequently asked questions
How many bags of urea per acre for wheat?
For a 48 kg nitrogen per acre recommendation, roughly 2 bags of 45 kg urea per acre after deducting the nitrogen supplied by DAP. Enter your own recommendation and area above for the exact figure.
Does DAP contain nitrogen?
Yes — 18% nitrogen alongside 46% phosphorus. This is why applying a full urea dose on top of full DAP over-applies nitrogen. The calculator deducts it automatically.
What does 48:24:16 mean?
Kilograms per acre of nitrogen, phosphorus as P₂O₅, and potassium as K₂O. These are nutrient quantities, not fertiliser quantities — which is exactly the conversion this tool performs.
Should I apply all fertiliser at sowing?
Phosphorus and potassium are usually applied fully at sowing as a basal dose. Nitrogen should be split, with part at sowing and the rest as top dressing with irrigation, because urea applied all at once is substantially lost.