The three numbers on a fertilizer bag are its NPK grade: the percentage of nitrogen (N), phosphorus (P₂O₅) and potassium (K₂O). Here is how to read them and choose a ratio that fits your crop, instead of buying whatever is on the shelf.
In short
- The numbers are percentages by weight, always in the order N-P-K.
- A "balanced" fertilizer such as 19-19-19 has the same share of each.
- Nitrogen-heavy grades push leaf growth, phosphorus-heavy grades help roots and flowers, potassium-heavy grades help fruit and stress tolerance.
- A soil test tells you which ratio you actually need.
Reading the grade
| Grade | N | P₂O₅ | K₂O | Typical use |
|---|---|---|---|---|
| 46-0-0 (urea) | 46% | 0 | 0 | Nitrogen top-dressing |
| 18-46-0 (DAP) | 18% | 46% | 0 | Phosphorus at planting |
| 0-0-60 (MOP) | 0 | 0 | 60% | Potassium |
| 19-19-19 | 19% | 19% | 19% | Balanced feed, often as a soluble fertilizer |
| 12-32-16 | 12% | 32% | 16% | Phosphorus-rich starter |
| 10-10-10 | 10% | 10% | 10% | General purpose |
Ratio versus grade
10-10-10 and 20-20-20 have the same ratio (1:1:1) but 20-20-20 is twice as strong. When you compare products, compare the ratio first, then the strength and price per kg of nutrient.
Matching the ratio to the crop stage
| Stage | Usually needs more |
|---|---|
| Seedling and early growth | Phosphorus (roots) and some nitrogen |
| Leafy growth | Nitrogen |
| Flowering and fruit or grain fill | Potassium (and enough phosphorus) |
Exact needs depend on crop, soil and yield target, so use a soil test and local advice.
Common mistakes
- Using one grade for every crop and stage.
- Adding more of a nutrient the soil already has.
- Ignoring pH, which can lock up phosphorus and other nutrients.
- Skipping organic matter.
How Famo AI helps
Famo AI shows nitrogen, phosphorus and potassium results as low, in range or high, so you can choose a ratio from your own soil data. Compare fields and seasons in the web dashboard. Our NPK results guide goes deeper.
Get Famo AI on Google Play or try the live demo, no sign-up needed.
Frequently asked questions
What does NPK 19-19-19 mean?
It contains 19% nitrogen, 19% phosphorus (as P₂O₅) and 19% potassium (as K₂O): a balanced fertilizer.
Is a higher NPK number always better?
No. A higher number is only a more concentrated product. The right ratio depends on your soil and crop.
Which NPK is best for flowering?
Flowering and fruiting usually benefit from more phosphorus and potassium and less nitrogen, but check your soil test.
