Fertilizer Calculator
Pounds of fertiliser for a target nitrogen rate and NPK.
Enter your values
Enter the area in sq ft.
Enter the target nitrogen in lb N/1000 sq ft.
Enter the nitrogen % (first npk number) in %.
Enter the bag size in lb.
Enter the cost per bag in $.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Fertiliser needed
- 20.83 lb
- Rate per 1,000 sq ft
- 4.17 lb
- Bags to buy
- 1
- Cost
- $35.00
- Actual N applied
- 5 lb total
Working
- 11 / 0.24 = 4.17 lb per 1000 ft2 x 5
Quick answer
Product needed = target N per 1,000 sq ft divided by the nitrogen percentage, multiplied by the area in thousands of square feet.
lb product = (target N / (N% / 100)) x area/1000
At a glance
| What it does | Pounds of fertiliser for a target nitrogen rate and NPK. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Area, Target nitrogen, Nitrogen % (first NPK number), Bag size, Cost per bag |
| Main output | Fertiliser needed |
| Formula | lb product = (target N / (N% / 100)) x area/1000 |
| Cost | Free — no sign-up, no download |
How to use the Fertilizer Calculator
- 1Read the first NPK number on the bag - that is the nitrogen percentage.
- 2Choose a target rate: 0.5 to 1 lb N per 1,000 sq ft per application is typical for lawns.
- 3Spread half in one direction and half at right angles for even coverage.
Inputs explained
- Area(sq ft)
- Enter the area in sq ft.
- Target nitrogen(lb N/1000 sq ft)
- Enter the target nitrogen in lb N/1000 sq ft.
- Nitrogen % (first NPK number)(%)
- Enter the nitrogen % (first npk number) in %.
- Bag size(lb)
- Enter the bag size in lb.
- Cost per bag($)
- Enter the cost per bag in $.
Worked example
Using the values the calculator loads with:
Inputs
- Area5000 sq ft
- Target nitrogen1 lb N/1000 sq ft
- Nitrogen % (first NPK number)24 %
- Bag size40 lb
- Cost per bag35 $
Results
- Fertiliser needed20.83 lb
- Rate per 1,000 sq ft4.17 lb
- Bags to buy1
- Cost$35.00
- Actual N applied5 lb total
- 1 / 0.24 = 4.17 lb per 1000 ft2 x 5
Frequently asked questions
How much nitrogen per year does a lawn need?
Most cool-season lawns want 2 to 4 lb of nitrogen per 1,000 sq ft per year, split across 3 to 5 applications.
What if I apply too much?
You risk burning the grass and leaching nitrogen into groundwater. Slow-release products are far more forgiving at higher rates.
What do I need to enter into the Fertilizer Calculator?
Just 5 values: area, target nitrogen, nitrogen % (first npk number), bag size, cost per bag. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Fertilizer Calculator work out the answer?
Product needed = target N per 1,000 sq ft divided by the nitrogen percentage, multiplied by the area in thousands of square feet. It applies the formula lb product = (target N / (N% / 100)) x area/1000 and shows the working so you can check each step by hand.
Is the Fertilizer Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.