NPK Fertilizer Calculator (Percent to Application Rate with Blending)

Q: "I want to combine two or more fertilizers."

"Add two or more fertilizers and use the \"No shortage, lowest total cost\" mode. The tool finds a blend that does not fall short. If any price is missing, it minimizes total application rate instead."

Q: "My units are different."

"Use the unit toggle to switch between kg/ha and lb/acre. Inputs and results stay in the selected unit system."

Q: "My fertilizer label uses P2O5 and K2O."

"Switch between elemental P/K and the common P2O5/K2O basis. Internally the tool normalizes everything to elemental P and K."

Q: "What if nutrients are still short?"

"The tool highlights shortages in red, explains the likely cause, such as no source for that nutrient or a max-rate limit, and shows an adjustment suggestion."

Calculate the fertilizer amount needed to hit target N-P-K nutrient rates from product grades such as 10-10-10.

Accepts 10-10-10 style input Shows shortages in blends Switches between kg/ha and lb/acre Supports share links and print view

How to use

Set the unit, P and K basis, and loss rate, then enter target N, P, and K nutrient rates.
Add one or more fertilizers and enter the grade, and optionally price and max application rate.
Choose a calculation mode and review shortages, excess, and adjustment suggestions.

Inputs

Target nutrient rates: enter N, P, and K in the same unit system.
Grade input: use a 10-10-10 style entry or separate N/P/K fields.
Blending: add rows to combine multiple fertilizers.
Loss rate: adjust required application for expected nutrient loss.
Cost: when prices are entered, the tool also estimates total cost.

How to read the output

The summary shows immediately whether the target is met, short, or excessive.
The fertilizer list shows how much of each product to apply.
The nutrient table compares target, applied, effective, and delta values.
When nutrients are short, the adjustment panel suggests the next step.

Quick examples

10-10-10 for 60-60-60

Input

Unit kg/ha, P/K basis set to elemental P and K, loss rate 0%, target N=60, P=60, K=60, one fertilizer row with 10-10-10

Output

Required fertilizer rate 600.0 kg/ha, target met, no shortage

Urea + phosphate + potash with no shortage

Input

Unit kg/ha, P/K basis set to P2O5 and K2O, loss rate 0%, target N=60, P2O5=60, K2O=60, plus rows for urea 46-0-0, phosphate 0-20-0, and potash 0-0-60

Output

Urea 130.4 kg/ha, phosphate 300.0 kg/ha, potash 100.0 kg/ha, target met

How the calculation works

Nutrient fraction f = nutrient percent / 100
Single-fertilizer amount A = target rate / ((1 - loss rate) x nutrient fraction)
For blends, the tool searches for a combination that satisfies the no-shortage or priority-match rule while minimizing total cost or total application rate.

Frequently Asked Questions

I want to combine two or more fertilizers.

Add two or more fertilizers and use the "No shortage, lowest total cost" mode. The tool finds a blend that does not fall short. If any price is missing, it minimizes total application rate instead.

My units are different.

Use the unit toggle to switch between kg/ha and lb/acre. Inputs and results stay in the selected unit system.

My fertilizer label uses P2O5 and K2O.

Switch between elemental P/K and the common P2O5/K2O basis. Internally the tool normalizes everything to elemental P and K.

What if nutrients are still short?

The tool highlights shortages in red, explains the likely cause, such as no source for that nutrient or a max-rate limit, and shows an adjustment suggestion.

Important notes

This tool performs calculation only. Follow soil analysis, local fertilizer standards, and crop recommendations when making a fertilizer plan.
Excess fertilization can increase environmental load or harm crop growth. Check local rules and field conditions.
The loss rate is a simplified model that applies the same percentage to N, P, and K. Actual behavior can differ by nutrient.