Fertilizer Calculator 🌿 – NPK Rate, Bags & Cost for Lawn and Garden
Find out how much fertilizer you need per square foot, marla, kanal or acre. Enter your area and NPK grade to get the exact weight, number of bags and cost in seconds.
Don't know your area? Enter length × width
Free Fertilizer Calculator for Lawn, Garden and Farm Plots
Our fertilizer calculator tells you exactly how much fertilizer to buy and spread so your plants get what they need and nothing goes to waste. Enter your area in square feet, square meters, marla, kanal or acres, pick a fertilizer such as urea, DAP or NPK 10-10-10, set the nutrient rate, and the tool shows the total weight, the number of bags and the estimated cost. It also shows how much nitrogen, phosphate and potash your application actually delivers.
If you have ever wondered how much fertilizer per 1,000 sq ft, how many bags of fertilizer you need for your lawn, or how much urea to use per kanal, this NPK fertilizer calculator does the maths for you in seconds. It runs in your browser, needs no signup and works on mobile and desktop.
How to Use This Fertilizer Calculator (Step by Step)
- Choose a mode. Pick By Nutrient Target (NPK) if you know how much nitrogen, phosphate or potash you want to apply. Pick By Bag Label Rate if your bag already tells you how many pounds or kilograms of product to spread per area.
- Enter your area and unit. If you only know the length and width, open the length × width helper and the calculator converts it for you.
- Select your fertilizer. Choose a common product or enter the N-P-K percentages printed on your bag.
- Set the application rate. Type a rate or tap a quick preset. A common lawn target is 1 lb of nitrogen per 1,000 sq ft per application.
- Add bag size, price and number of applications (optional). This unlocks the bag count, cost and season total.
- Press Calculate Total Needed. Read the total weight in pounds and kilograms, the bags to buy and the nutrients delivered.
What This NPK Fertilizer Calculator Tells You
- Total fertilizer required in pounds and kilograms, and in grams for small areas.
- Bags to buy rounded up to whole bags, so you never run short halfway through.
- Estimated cost based on your price per bag.
- Season total when you split feeding into several applications.
- Nutrients delivered per 1,000 sq ft and across your whole area for nitrogen (N), phosphate (P₂O₅) and potash (K₂O).
- A worked formula so you can see exactly how the answer was reached.
How to Calculate Fertilizer per Square Foot (The Formula)
Fertilizer labels show the percentage of each nutrient by weight, so you cannot simply multiply area by the nutrient you want. You have to divide by the nutrient percentage first. The standard formula is:
Fertilizer needed (lb) = (nutrient rate per 1,000 sq ft ÷ nutrient %) × (area ÷ 1,000)
Example 1: A 5,000 sq ft lawn with urea
You want 1 lb of nitrogen per 1,000 sq ft. Urea is 46% nitrogen, so the maths is (1 ÷ 0.46) × (5,000 ÷ 1,000) = 10.87 lb, which is about 4.93 kg of urea.
Example 2: One kanal (5,445 sq ft)
With the same 1 lb N per 1,000 sq ft rate and urea, one kanal needs (1 ÷ 0.46) × 5.445 = 11.84 lb, or about 5.4 kg. One marla (272.25 sq ft) needs roughly 0.27 kg.
Example 3: How far does a bag go?
A 50 lb bag of 10-10-10 contains 10% nitrogen, which is 5 lb of actual nitrogen. At 1 lb N per 1,000 sq ft, that single bag covers about 5,000 sq ft.
How to Read the NPK Numbers on a Fertilizer Bag
Every bag shows three numbers, called the fertilizer grade. They are the percentage by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O), always in that order. Nitrogen drives leaf growth and green colour. Phosphorus supports roots, flowers and fruit. Potassium helps plants handle heat, drought and cold. A 46-0-0 product such as urea is pure nitrogen, DAP at 18-46-0 is rich in phosphate, and potash at 0-0-60 supplies only potassium.
Remember the difference between product weight and nutrient weight. Fifty pounds of urea is not fifty pounds of nitrogen; it contains about 23 lb of nitrogen. Need to work with percentages by hand? Try our free percentage calculator.
Fertilizer Needed for 1 lb of Nitrogen per 1,000 Sq Ft
This table shows how much of each common product you need to deliver the standard 1 lb of nitrogen per 1,000 sq ft. Grades vary by brand, so always check your own bag.
| Fertilizer | Grade (N-P-K) | Per 1,000 sq ft | Per kanal (5,445 sq ft) |
|---|---|---|---|
| Urea | 46-0-0 | 2.17 lb (0.99 kg) | 11.84 lb (5.37 kg) |
| CAN | 26-0-0 | 3.85 lb (1.74 kg) | 20.94 lb (9.50 kg) |
| Ammonium Sulfate | 21-0-0 | 4.76 lb (2.16 kg) | 25.93 lb (11.76 kg) |
| DAP (also adds phosphate) | 18-46-0 | 5.56 lb (2.52 kg) | 30.25 lb (13.72 kg) |
| Lawn Fertilizer | 28-0-6 | 3.57 lb (1.62 kg) | 19.44 lb (8.82 kg) |
| Lawn Fertilizer | 24-8-12 | 4.17 lb (1.89 kg) | 22.69 lb (10.29 kg) |
| NPK Balanced | 20-20-20 | 5.00 lb (2.27 kg) | 27.23 lb (12.35 kg) |
| NPK Balanced | 10-10-10 | 10.00 lb (4.54 kg) | 54.45 lb (24.70 kg) |
Area Units: Square Feet, Marla, Kanal and Acre
Fertilizer rates are usually given per 1,000 sq ft or per acre, while land in Pakistan is often measured in marla and kanal. This calculator converts everything for you using these values: 1 marla = 272.25 sq ft, 1 kanal = 20 marla = 5,445 sq ft, 1 acre = 43,560 sq ft and 1 square meter = 10.764 sq ft. Some regions use a slightly different marla, so if your local marla differs, enter your area in square feet instead. For other conversions, use our free unit converter.
Common Mistakes That Waste Fertilizer or Burn Plants
- Guessing the area. Measure your lawn or bed, and subtract areas that will not be fertilized, such as the house, paths and driveways.
- Mixing up product weight and nutrient weight. Always divide the nutrient rate by the nutrient percentage.
- Applying too much nitrogen at once. Quick-release nitrogen can scorch leaves. Many extension guides suggest staying near 1 lb N per 1,000 sq ft per application and splitting larger amounts.
- Skipping the soil test. Your soil may already be high in phosphorus or potassium, so extra amounts are wasted money.
- Uneven spreading. Apply half the amount in one direction and half at a right angle to avoid stripes.
- Not watering in, or fertilizing before heavy rain. Runoff wastes product and pollutes waterways.
Tips for Better Results
Start with a soil test, then use this calculator to turn the recommended nutrient rates into real product weights. Choose slow-release nitrogen for steadier feeding and less burn risk, split heavy feeding into several lighter applications, and water the fertilizer in after spreading. Plan the timing of your applications with the days between dates calculator, and compare bulk prices with the discount calculator before you buy.
Why Use This Fertilizer Calculator?
Many fertilizer calculators only handle a single nutrient in US units. This one supports nitrogen, phosphate and potash targets, works with marla, kanal, acre, hectare and metric units, converts the result into bags and cost, and shows what every application delivers. It also keeps a simple label-rate mode for when your bag already gives you a rate.
More Free Tools You May Like
This calculator is part of our library of 60+ free online tools. Explore more from the Free Image Tools homepage, or try these related tools: the food calorie calculator for the harvest you grow, the AI food scanner, the unit converter and the percentage calculator.
Frequently Asked Questions About Fertilizer Calculators
How much fertilizer do I need per square foot?
It depends on the nutrient you want to apply and the grade of the product. A common lawn target is about 1 lb of nitrogen per 1,000 sq ft per application. Divide that by the nitrogen percentage on the bag to get pounds of product per 1,000 sq ft, which is about 2.2 lb for urea (46-0-0).
How do I calculate fertilizer for my lawn or garden?
Use this formula: fertilizer needed (lb) = (target nutrient rate per 1,000 sq ft ÷ nutrient percentage) × (area ÷ 1,000). For example, 1 lb of nitrogen per 1,000 sq ft on a 5,000 sq ft lawn with 46% urea is (1 ÷ 0.46) × 5 = 10.87 lb of urea.
How many bags of fertilizer do I need?
Enter your bag size and the calculator divides the total fertilizer needed by the bag weight and rounds up to the next whole bag. If you enter a price per bag, it also shows the estimated cost.
What do the three numbers on a fertilizer bag mean?
They show the percentage by weight of nitrogen (N), phosphate (P2O5) and potash (K2O). A 50 lb bag of 10-10-10 contains 5 lb of nitrogen, 5 lb of phosphate and 5 lb of potash.
How much urea do I need per kanal or marla?
To apply 1 lb of nitrogen per 1,000 sq ft, you need about 5.4 kg of urea for one kanal (5,445 sq ft) and about 0.27 kg for one marla (272.25 sq ft). Your soil test or crop advice may call for a different rate, so adjust the target in the calculator.
What is a safe amount of nitrogen for one application?
For quick-release nitrogen on lawns, many extension guides suggest staying near 1 lb of nitrogen per 1,000 sq ft per application. If you need more over a season, split it into several lighter applications and water it in.
Should I do a soil test before fertilizing?
A soil test is the best way to know which nutrients your soil actually needs. It can show if you can skip phosphorus or potassium and only apply nitrogen, which saves money and reduces runoff.
Can I use this fertilizer calculator for a vegetable garden, flowers or trees?
Yes. The math works for any area you fertilize. Just enter the planted area and use the nutrient rate recommended for your crop, soil test or the fertilizer label.
What is the difference between fertilizer weight and nutrient weight?
Fertilizer weight is the total weight of the product, while nutrient weight is the amount of N, P2O5 or K2O inside it. For example, 50 lb of urea contains about 23 lb of nitrogen.
Is this fertilizer calculator free and private?
Yes. It is free with no signup, and all calculations run in your browser, so nothing you enter is uploaded.
Disclaimer: This calculator provides estimates for general guidance. Fertilizer grades and crop needs vary, so always follow the product label, your soil test results and local agricultural advice.