Fertilizer Rate Calculator (lbs per acre)

A fertilizer rate calculator converts a target nutrient application (like 120 lb N/acre) into an actual product rate based on the fertilizer analysis (like 32-0-0, 46-0-0, or 10-34-0). This is one of the most common farm math tasks—especially when switching products or matching a recommendation to what’s available.

This guide explains the fertilizer analysis label, the core formula, and practical examples for nitrogen, phosphorus, and blended fertilizers.

What Does 32-0-0 or 10-34-0 Mean?

Fertilizer grades are written as N-P-K:

Example: 32-0-0 contains 32% nitrogen by weight (or by volume equivalents for some liquids depending on density).

Many agronomic recommendations are expressed as N, P2O5, and K2O. Always confirm what units your recommendation is using.

---

Fertilizer Rate Formula

The basic conversion is:

Product rate (lb/acre) = (Desired nutrient lb/acre) ÷ (Nutrient fraction)

Convert the fertilizer percentage into a fraction:

Nutrient fraction = (Percent nutrient) ÷ 100
---

Example: Apply 120 lb N/acre Using 32-0-0

Target nitrogen: 120 lb N/acre

Fertilizer grade: 32-0-0 (32% N)

Product rate = 120 ÷ 0.32 = 375 lb/acre of 32-0-0

If you’re using liquid UAN, you may also want the calculator to convert lb/acre into gal/acre using product density.

---

Example: Apply 100 lb N/acre Using Urea (46-0-0)

Target nitrogen: 100 lb N/acre

Fertilizer grade: 46-0-0 (46% N)

Product rate = 100 ÷ 0.46 = 217.4 lb/acre of urea
---

Example: Apply Phosphorus Using 10-34-0

Many recommendations call for P2O5. If your goal is 60 lb P2O5/acre and you’re using 10-34-0:

Product rate = 60 ÷ 0.34 = 176.5 lb/acre of 10-34-0
---

Blends: When One Product Supplies Multiple Nutrients

For a blend like 19-19-19, each nutrient is 19%.

If you apply 200 lb/acre of 19-19-19, you’re applying:

N applied = 200 × 0.19 = 38 lb N/acre
P2O5 applied = 200 × 0.19 = 38 lb/acre
K2O applied = 200 × 0.19 = 38 lb/acre

A fertilizer rate calculator can help solve this in either direction: (1) rate → nutrients, or (2) nutrient target → rate.

---

Common Fertilizer Products (Quick Reference)

Product Grade Primary Use
UAN 28-0-0 or 32-0-0 Nitrogen (liquid)
Urea 46-0-0 Nitrogen (dry)
Ammonium Nitrate 34-0-0 Nitrogen (dry)
MAP 11-52-0 Phosphorus starter
DAP 18-46-0 Phosphorus + nitrogen
Potash 0-0-60 Potassium (K)
---

Use Our Free Fertilizer Rate Calculator

Convert nutrient targets to product rates in seconds:

Open the Free Fertilizer Rate Calculator

Use it for nitrogen, phosphorus (P2O5), potassium (K2O), and common products like UAN, urea, MAP, DAP, and potash.

---

Frequently Asked Questions

Why is phosphorus listed as P2O5?

Fertilizer labels commonly use oxide forms: P2O5 for phosphate and K2O for potash. Many agronomic recommendations match these label forms.

How do I convert liquid fertilizer to gallons per acre?

You need the product density (lb/gal). Many UAN products are around 10–11 lb/gal, but it varies. A calculator can convert lb/acre to gal/acre when you enter density.

What’s the most common mistake when calculating fertilizer rate?

Mixing up nutrient units (N vs N-P-K label), forgetting to convert percent to a fraction, or using a P recommendation when you need P2O5 (or vice versa).

---

← Back to Calculator.Farm