A fertilizer calculator per acre that turns N-P-K into bags
A soil test or a crop recommendation tells you how many kilograms of nutrients a field needs — for example 150-60-40 kg of N, P₂O₅ and K₂O per hectare. A fertilizer dealer sells products: urea, DAP, SSP, MOP and NPK complexes in 45 and 50 kg bags. This fertilizer calculator bridges the two. Type the dose, choose your fertilizers and field size in acres, hectares, bigha, guntha, cent or kanal, and it shows the kilograms and number of bags (बोरी) of each product, with the working for every step.
The calculation follows the order agronomists use: the phosphorus fertilizer is worked out first because DAP and complexes also carry nitrogen (and some carry potash), then potash for the K₂O still needed, and finally urea for the remaining nitrogen. Forgetting the 18% nitrogen inside DAP is the most common reason people over-apply urea. Everything runs in your browser; nothing is uploaded.
How to use the fertilizer calculator
- Pick an example recommendation or keep My soil-test / KVK recommendation and type the N, P₂O₅ and K₂O figures from your Soil Health Card or package of practices.
- Set Dose is given in to kg per hectare or kg per acre, exactly as written on your recommendation.
- Enter your field area and unit. For bigha, type the size of one bigha in your area in sq ft.
- Choose where phosphorus, potash and the remaining nitrogen come from — DAP or SSP, MOP or SOP, urea, ammonium sulphate or CAN.
- Read the kg and bags for your field, the per-acre and per-hectare amounts, and the nutrient check. Open Bag sizes and prices to change bag weights or add prices for a cost estimate.
Fertilizer Calculator features
Accounts for nitrogen in DAP
The N supplied by DAP, MAP, APS or an NPK complex is subtracted before urea is calculated, so the total matches the recommendation.
Indian fertilizer grades
Urea 46% N, DAP 18-46-0, SSP 16% P₂O₅, MOP 60% K₂O, SOP, ammonium sulphate, CAN and complexes 10-26-26, 12-32-16, 14-35-14 and 20-20-0 at their Fertiliser Control Order grades.
Acre, hectare and bigha
Exact conversions for acre, hectare, guntha, cent, kanal, m² and sq ft, plus a bigha whose size you set.
Bags and loose kg
Shows “6 bags + 5 kg” as well as decimal bags, with the 45 kg urea bag and 50 kg bags for the rest by default.
Nutrient check and warnings
A table compares what the products supply with the target and flags surplus nitrogen or potash from a complex.
The formula, step by step
Fertilizer needed (kg) = nutrient needed (kg) ÷ nutrient content (%) × 100. For wheat at 150-60-40 kg/ha with DAP, MOP and urea:
- DAP for phosphorus: 60 ÷ 46% = 130.4 kg DAP per ha. It also supplies 130.4 × 18% = 23.5 kg N.
- MOP for potash: 40 ÷ 60% = 66.7 kg MOP per ha.
- Urea for the rest of the nitrogen: (150 − 23.5) ÷ 46% = 275.0 kg urea per ha.
- Per acre: multiply by 0.4047 — about 52.8 kg DAP, 27.0 kg MOP and 111.3 kg urea, or roughly one bag of DAP, half a bag of MOP and two and a half bags of urea.
Nutrient content of common fertilizers
Grades are the minimum specifications in Schedule I of the Fertiliser (Control) Order, 1985, as read on 19 October 2026. To compare or blend products by their N-P-K numbers, use the NPK calculator.
| Fertilizer | N % | P₂O₅ % | K₂O % | Also |
|---|---|---|---|---|
| Urea | 46 | — | — | 45 kg bag since 2018 |
| DAP (diammonium phosphate) | 18 | 46 | — | |
| SSP (single superphosphate) | — | 16 | — | 11% sulphur |
| MOP (muriate of potash) | — | — | 60 | |
| SOP (sulphate of potash) | — | — | 50 | 17.5% sulphur |
| Ammonium sulphate | 20.6 | — | — | 23% sulphur |
| CAN (calcium ammonium nitrate) | 25 | — | — | |
| NPK 10-26-26 / 12-32-16 / 14-35-14 | 10 / 12 / 14 | 26 / 32 / 35 | 26 / 16 / 14 | complexes |
Where the example doses come from
The rice examples are the blanket recommendations on the Tamil Nadu Agricultural University Agritech portal (updated December 2022), which TNAU says to use only when soil-test or leaf-colour-chart based doses are not available. The wheat example, 150-60-40 kg/ha for irrigated, timely sown wheat in the North Western Plains Zone, is the recommended dose cited by ICAR-IIWBR scientists in Indian Farming. Your own state or district recommendation, and above all your soil test, should replace them.
Fertilizer Calculator FAQ
How much urea per acre do I need?
It depends on your nitrogen dose and on whether DAP is also applied. For 150 kg N/ha with 60 kg P₂O₅ from DAP, the calculator gives about 111 kg urea per acre — two bags plus about 21 kg. Without DAP, 150 kg N/ha would need about 132 kg urea per acre.
How do I calculate fertilizer based on a soil test?
Take the N, P₂O₅ and K₂O doses printed on your Soil Health Card for your crop, type them in with the right unit (usually kg/ha), and the fertilizer calculator converts them into products and bags for your field area.
How much DAP per acre for 60 kg P₂O₅ per hectare?
60 ÷ 0.46 = 130.4 kg DAP per hectare, or 52.8 kg per acre — just over one 50 kg bag.
Why is less urea needed when I use DAP?
DAP contains 18% nitrogen, so every 50 kg bag supplies 9 kg N. The calculator subtracts it before working out urea.
Can I use SSP instead of DAP?
Yes. Choose SSP under Phosphorus from. SSP has 16% P₂O₅ and no nitrogen, so you need about three times as much product, more urea, and you also get about 11% sulphur.
How big is a bigha?
It varies by state and even by district — from about a fifth of an acre to more than half an acre. Enter the sq ft of one bigha in your area; the default of 14,400 sq ft is the West Bengal and Assam bigha.
Is this fertilizer advice?
No. It is arithmetic on the dose you enter. Ask your KVK, agriculture officer or state agricultural university for the right dose and timing for your crop and soil.