Calculate Weight of N in Urea and in Ammonium Nitrate
Use this calculator to determine the exact amount of Nitrogen (N) supplied by your fertilizer application. Compare efficiency and cost between Urea and Ammonium Nitrate to optimize your agricultural nutrient management.
Nitrogen Content Calculator
Urea (CO(NH₂)₂)
Ammonium Nitrate (NH₄NO₃)
Select the nitrogen source you are using.
Enter the total weight of the fertilizer bag or bulk amount.
Please enter a positive weight.
Kilograms (kg)
Pounds (lbs)
Metric Tons
Select the unit for the weight entered above.
Standard Urea is 46%; Standard AN is 33.5-34%.
Please enter a valid percentage (0-100).
Enter the price paid for the total weight to calculate cost per unit of N.
Total Nitrogen (N) Weight
46.00 kg
Pure Elemental Nitrogen
Purity Factor0.46
Inert/Carrier Weight54.00 kg
Cost per unit NN/A
Formula Used: Weight of N = Total Product Weight × (Nitrogen Grade / 100)
Composition Breakdown
Detailed Analysis
Component
Weight
Percentage
breakdown of active nitrogen versus carrier material in the selected fertilizer volume.
What is Calculating Weight of N in Urea and Ammonium Nitrate?
Calculating the weight of Nitrogen (N) in Urea and in Ammonium Nitrate is a fundamental task for farmers, agronomists, and turf managers. It involves determining exactly how much elemental nitrogen is delivered to the soil when a specific weight of fertilizer product is applied. This is critical because crops require Nitrogen, not "Urea" or "Ammonium Nitrate" per se; the latter are simply the chemical carriers.
Urea (CO(NH₂)₂) and Ammonium Nitrate (NH₄NO₃) are two of the most common nitrogen sources in agriculture. However, they have different chemical compositions and densities. Urea typically contains 46% nitrogen, making it the most concentrated solid nitrogen fertilizer. Ammonium Nitrate usually contains between 33.5% and 34% nitrogen. Understanding these differences is essential for converting "product weight" into "nutrient weight," ensuring crops receive the correct dosage without wastage or environmental runoff.
This calculation is vital for anyone engaging in precision agriculture or managing a fertilizer budget. Misinterpreting the weight of N can lead to under-fertilization (poor yields) or over-fertilization (soil toxicity and financial loss).
Formula and Mathematical Explanation
To calculate the weight of N in urea and in ammonium nitrate, we use a straightforward stoichiometric calculation based on the percentage of nitrogen in the compound. The general formula is:
Weight of N = Total Weight of Fertilizer × (Percentage of N / 100)
Derivation from Atomic Mass
The percentage figures (46% for Urea, 34% for AN) are derived from the molar mass of the elements:
Nitrogen (N): 14.007 g/mol
Hydrogen (H): 1.008 g/mol
Carbon (C): 12.011 g/mol
Oxygen (O): 15.999 g/mol
Compound
Chemical Formula
Molar Mass (g/mol)
Mass of N (g/mol)
% Nitrogen (Pure)
Urea
CO(NH₂)₂
60.06
28.02 (2 atoms)
46.65% (approx 46%)
Ammonium Nitrate
NH₄NO₃
80.04
28.02 (2 atoms)
35.00% (approx 33.5-34%)
Atomic mass derivation for nitrogen content.
Note: Commercial Ammonium Nitrate often has a slightly lower percentage (33.5% or 34%) than the pure chemical form due to the addition of stabilizing agents or clay coatings to improve handling.
Practical Examples (Real-World Use Cases)
Example 1: Top-Dressing Wheat with Urea
A farmer needs to apply 50 kg of actual Nitrogen per hectare to a wheat field. They have bags of granular Urea (46-0-0). How much physical product is required?
Target N: 50 kg
Source: Urea (46% N)
Calculation: Weight of Product = Target N / 0.46
Result: 50 / 0.46 = 108.7 kg of Urea
Using the calculator above in reverse logic helps verify: If you input 108.7 kg of Urea, the result shows ~50 kg of N.
Example 2: Cost Comparison between Urea and AN
Suppose Urea costs $600 per ton and Ammonium Nitrate (33.5%) costs $500 per ton. Which is the cheaper source of Nitrogen?
Urea:
1 Ton Product = 1000 kg
Mass of N = 1000 × 0.46 = 460 kg N
Cost per kg N = $600 / 460 = $1.30 per kg N
Ammonium Nitrate:
1 Ton Product = 1000 kg
Mass of N = 1000 × 0.335 = 335 kg N
Cost per kg N = $500 / 335 = $1.49 per kg N
Conclusion: Even though Ammonium Nitrate is cheaper per ton, Urea is the cheaper source of Nitrogen in this scenario. This demonstrates why calculating the weight of N is crucial for financial efficiency.
How to Use This Calculator
This tool is designed to be intuitive for quick field calculations or office planning.
Select Fertilizer Type: Choose between Urea or Ammonium Nitrate. This automatically sets the standard purity percentage (46% or 33.5%).
Enter Product Weight: Input the total mass of the fertilizer bag or bulk load you are analyzing.
Select Unit: Choose kg, lbs, or tons. The math remains consistent regardless of the unit.
Verify/Adjust Grade: If your specific fertilizer label says 45% or 34%, adjust the "Nitrogen Grade" field accordingly.
Optional Cost: Enter the total price of the product to see the price per unit of Nitrogen.
Analyze Results: View the highlighted Total Nitrogen Weight, the breakdown table, and the visual chart to understand the nutrient density.
Key Factors That Affect Nitrogen Results
When you calculate weight of n in urea and in ammonium nitrate, several real-world factors can influence the effective nitrogen delivered to the plant versus the theoretical calculation.
1. Purity and Fillers
Commercial fertilizers are rarely 100% pure. They contain conditioners to prevent caking (like clay or limestone). This is why Ammonium Nitrate is often sold as 33.5% rather than its pure 35%. Always check the guaranteed analysis on the bag tag.
2. Volatilization (Urea Specific)
Urea is susceptible to volatilization. If applied to the surface without rainfall or incorporation, a significant percentage of N (up to 40% in worst cases) can be lost to the atmosphere as ammonia gas. While the calculator gives the weight of N in the bag, the weight of N absorbed by the plant depends on application method.
3. Hygroscopicity
Both fertilizers attract moisture from the air. If stored improperly, the weight of the bag may increase due to water weight, diluting the percentage of N by weight. The calculator assumes dry product.
4. Leaching Potential
Ammonium Nitrate contains Nitrate-N, which is highly mobile in water and prone to leaching. Urea must first convert to ammonium and then nitrate. This timing affects when the calculated weight of N becomes available to the roots.
5. Acidification Effects
Nitrogen fertilizers acidify the soil over time. Ammonium Nitrate is less acidifying per unit of N compared to Urea (because Urea transformation releases H+ ions). This long-term soil health cost is a "hidden factor" beyond the simple weight calculation.
6. Cost Efficiency
As shown in the examples, the price per bag is misleading. Transport costs also factor in; since Urea is more concentrated, you transport less physical weight for the same amount of Nitrogen, often reducing freight costs significantly.
Frequently Asked Questions (FAQ)
Why is Urea 46% N and not 100%?
Urea is a chemical compound (CO(NH₂)₂). The Nitrogen atoms are bonded to Carbon, Oxygen, and Hydrogen atoms. These other atoms make up the remaining 54% of the weight. You cannot have "100% Nitrogen" in solid form as Nitrogen is a gas (N₂) at standard temperature.
Can I mix Urea and Ammonium Nitrate?
Generally, no. Mixing them can lower the critical relative humidity of the blend, causing the mixture to absorb moisture rapidly and turn into a wet slush, making it impossible to spread.
Does the unit (kg vs lbs) change the percentage?
No. Percentage is a ratio. 46% of 100 lbs is 46 lbs; 46% of 100 kg is 46 kg. The calculator handles the units for labeling, but the ratio remains constant.
Is Ammonium Nitrate faster acting than Urea?
Yes. Half of the nitrogen in Ammonium Nitrate is in nitrate form (NO₃⁻), which is immediately available to plants. Urea must undergo hydrolysis and nitrification in the soil to become available, which takes time and depends on temperature.
How do I calculate liquid nitrogen fertilizer?
Liquid calculations differ because you must account for the density (weight per gallon/liter) of the liquid. This calculator is designed for solid forms of Urea and AN.
What is "UAN"?
UAN (Urea-Ammonium Nitrate) is a liquid solution mixture of Urea and Ammonium Nitrate. It typically contains 28%, 30%, or 32% Nitrogen. Calculating N for UAN requires knowing the solution density.
Why is the calculator result different from my soil test recommendation?
Soil tests recommend the amount of N required by the crop (e.g., 100 lbs N/acre). This calculator helps you determine how much product (e.g., 217 lbs of Urea) you need to buy to meet that recommendation.
Is Urea safer to store than Ammonium Nitrate?
Yes. Ammonium Nitrate is a strong oxidizer and has strict storage regulations due to explosion risks. Urea is generally considered non-hazardous for storage, though it should be kept dry.
Related Tools and Internal Resources
Expand your agricultural knowledge with our other specialized calculators and guides:
NPK Ratio Calculator – Determine the combined nutrient ratio when mixing different fertilizer sources.