Fertilizer Rate Calculator
Product needed for an area from the label analysis (N-P-K) and your target nutrient rate, with what each nutrient delivers, split applications and bags.
Product per 100 m² or 1000 ft² and for the whole area, the N, P₂O₅ and K₂O delivered, applications under a per-application cap and bag count — rate yours, not suggested.
Example: 250 m² with a 20-5-10 product at 1 kg N per 100 m²: 5 kg of product per 100 m², 12.5 kg in all (2 bags of 10 kg), delivering 2.5 kg N, 0.6 kg P₂O₅ and 1.25 kg K₂O — in 10 doses under a 0.5 kg cap.
The arithmetic
behind the label.
What the analysis means, how the product amount follows from a target rate, and why the rate is yours.
Label analysis
A fertilizer labelled 20-5-10 is 20 % N, 5 % P₂O₅ and 10 % K₂O by mass — that is the convention on labels, and the target rate is taken in the same form. Product per area = target rate ÷ (analysis % ÷ 100); for the plot, × area. The other two nutrients delivered are product × their percentages.
Applications and bags
If you enter a maximum product per application (from the label), the total is split into ⌈per-area amount ÷ cap⌉ equal doses. Bags = ⌈total ÷ bag mass⌉.
The rate is yours
No rate is suggested: the right amount depends on plant, soil test, season and local guidance, and over-application wastes money and pollutes run-off. Enter the rate from your soil test or the product directions. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Fertilizer label convention: analysis as N–P₂O₅–K₂O percentages by mass (AAPFCO / national labelling rules); rate arithmetic only
Last reviewed 20 September 2026. How results are checked: How we verify.