NPK Fertilizer Ratio Calculator

NPK fertilizer ratio

An NPK label reads %N : %P₂O₅ : %K₂O by mass. You'll run into a handful of common formulas. 10-10-10 is the balanced one most people reach for in a general garden, 4-14-8 is a planting base for fruit trees and ornamentals (heavy on P so roots take hold), 20-5-20 goes on as a top-dressing in hydroponics, and 0-46-0 is plain superphosphate. Nitrogen pushes leaf and stem growth, phosphorus backs up roots and flower formation, and potassium handles fruit quality and water balance. So 1 kg of 10-10-10 gives you 100 g N + 100 g P₂O₅ + 100 g K₂O. Leafy crops want plenty of N, while anything flowering or fruiting leans more on P and K.

Applications

This comes up in agriculture, gardening, fertigation, and home vegetable gardens. EMBRAPA publishes crop-specific NPK recommendations for coffee, soybean, citrus, lettuce and the like. With container plants, dilute to 1–2 g/L once a week. Out in the field, work from a prescription that's based on a soil analysis.

FAQ

Why P₂O₅ and K₂O instead of P and K? It's a holdover from the old oxide-based analysis. If you need the elemental figures: P = P₂O₅ × 0.436; K = K₂O × 0.830.

Can I mix two formulas? You can. Combining 10-10-10 with 4-14-8 doubles how many bags you go through, but it lets you land on a custom ratio. Just work out the weighted blend nutrient by nutrient.

NPK plus micronutrients? Plenty of formulas throw in S, Ca, Mg, B, Zn — look for "NPK + micros" on the label. You'll want it for sandy soils and intensive cropping.