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Convert your target N, P₂O₅ and K₂O rates into actual bagged fertilizer amounts using DAP (18-46-0), urea (46-0-0) and muriate of potash (0-0-60).
Enter the target nutrient rates per hectare and local fertilizer prices. The calculator decomposes the blend: DAP meets the phosphorus target, urea supplements nitrogen, and muriate of potash meets potassium demand.
You bought 500 kg of 15-15-15 to cover 150-60-100 kg NPK/ha and ran out of potassium halfway. Compound fertilizers force you to over-apply two nutrients to meet the third. Blending DAP + urea + potash matches nutrients exactly.
✓ Expert Reviewed: This calculator and its content have been reviewed by agricultural experts. Formulas are based on standard extension service recommendations. For site-specific advice, consult your local agronomist.
Enter target N, P₂O₅ and K₂O in kg per hectare, field area, and current prices for urea, DAP and muriate of potash. Click Calculate to see the split by product, total fertilizer weight and estimated cost.
This NPK calculator uses the standard extension decomposition: Fertilizer amount = target nutrient ÷ (nutrient fraction in fertilizer ÷ 100). It assumes DAP supplies both P₂O₅ (46%) and a small amount of N (18%), with urea making up the remaining N and MOP supplying all K₂O (60%).
DAP = target P₂O₅ ÷ 0.46. Nitrogen from DAP = DAP × 0.18. Urea needed = (target N − N from DAP) ÷ 0.46. Muriate of potash = target K₂O ÷ 0.60. Multiply each by field area and local price for cost.
Targets 150 N, 60 P₂O₅, 100 K₂O kg/ha. DAP = 60 ÷ 0.46 = 130 kg/ha, supplying 23 kg N. Remaining N = 127 kg → 276 kg urea/ha. MOP = 100 ÷ 0.60 = 167 kg/ha. Total = 573 kg/ha.
Common mistakes: confusing P₂O₅ with elemental P (multiply by 0.436), ignoring the nitrogen in DAP and over-application N, buying compound fertilizers that force over-application, and not accounting for road moisture or caking. Always weigh out a sample bag.
Fertilizer labels express nutrients as oxides by convention: N is elemental nitrogen, P₂O₅ is phosphorus pentoxide (elemental P = P₂O₅ × 0.436), K₂O is potassium oxide (elemental K = K₂O × 0.83). A 15-15-15 bag is 15% N, 15% P₂O₅ and 15% K₂O by weight.
Diammonium phosphate (DAP, 18-46-0) and monoammonium phosphate (MAP, 11-52-0) are the most common high-P sources. Rock phosphate is slow-release and only effective on acidic soils. Superphosphate is less concentrated and rarely used now.
Urea is 46% N by weight, so 100 kg N ÷ 0.46 = 217 kg urea. Ammonium sulfate (21% N) would require 476 kg, and calcium ammonium nitrate (27% N) requires 370 kg.
Blending single-nutrient sources (DAP + urea + MOP) is cheaper and more flexible when you have a soil test. Compound fertilizers (15-15-15, 20-10-10) are convenient for uniform blends but force you to over-apply nutrients where ratios do not match crop demand.
Multiply kg/ha by 0.892 to get lb/acre. Conversely, lb/acre × 1.12 = kg/ha. A target of 150 kg N/ha equals about 134 lb N/acre.