About the Lawn Fertilizer Calculator
Fertiliser bags show three numbers, such as 24-0-6. The first is the percentage of nitrogen, which is what the lawn mostly needs. To feed a lawn without burning it, you apply a set amount of nitrogen per 1,000 square feet. This calculator works out the weight of product to spread, from the area of the lawn, the nitrogen percentage and the rate, and the number of bags. Type the lawn area, the nitrogen percentage, the rate and the bag weight and the lawn fertilizer appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Lawn Fertilizer Calculator
- 1Enter the lawn area, the nitrogen percentage, the rate and the bag weight.
- 2Pick the units or options from the menus if the lawn fertilizer tool offers them.
- 3Read the lawn fertilizer in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the lawn fertilizer
Lawn owners use it to buy the right amount and avoid over-feeding, which wastes money, burns grass and washes nutrients into rivers. Lawn care businesses use the same sum to price a job.
A typical rate is 0.5 to 1 pound of nitrogen per 1,000 square feet per application, with several light feeds a year, not one heavy one. Slow-release products last longer and are safer than fast-release ones.
How the lawn fertilizer is worked out
Nitrogen needed = area ÷ 1,000 × rate (pounds per 1,000 sq ft). Product = nitrogen needed ÷ nitrogen percentage. Bags = product ÷ bag weight, rounded up. A 5,000 square foot lawn at 1 lb of nitrogen per 1,000 sq ft needs 5 lb of nitrogen. With a 24 percent nitrogen product, that is 20.8 lb of fertiliser (9.4 kg), one 25 lb bag.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Pounds, kilograms and bags
- Square feet or metres
- Four standard rates
Mistakes to avoid with lawn fertilizer
Always follow the instructions on the bag, which may be more conservative. The tool does not account for phosphorus or potassium, soil tests or local rules, some of which limit fertiliser use. Water the lawn after feeding as the label advises.
On phone and computer
On a phone, type into the boxes one after another and read the lawn fertilizer underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the lawn fertilizer move. The lawn fertilizer calculator works the same on both. Fertilizer amounts depend on the size of the lawn, so measure first. Use the Area Calculator for the size, the Topsoil Calculator to plan soil for bare patches, and the Mulch Calculator for beds beside the lawn.
Features
- Follow the bag label
- Light, frequent feeds
- Not for phosphorus or potassium
- Clear messages when the lawn fertilizer inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate lawn fertilizer?
Nitrogen needed = area ÷ 1,000 × rate (pounds per 1,000 sq ft). Product = nitrogen needed ÷ nitrogen percentage. Bags = product ÷ bag weight, rounded up. A 5,000 square foot lawn at 1 lb of nitrogen per 1,000 sq ft needs 5 lb of nitrogen. With a 24 percent nitrogen product, that is 20.8 lb of fertiliser (9.4 kg), one 25 lb bag.
What is the formula for lawn fertilizer?
Nitrogen needed = area ÷ 1,000 × rate (pounds per 1,000 sq ft). Product = nitrogen needed ÷ nitrogen percentage. Bags = product ÷ bag weight, rounded up. The lawn fertilizer calculator applies it exactly and rounds only the displayed answer to six significant figures.
What do the three numbers on the bag mean?
The percentages of nitrogen, phosphorus and potassium by weight.
How often should I fertilise?
Often two to four times a year for cool-season grass, but follow local advice.
What happens if I use too much?
The grass can burn, and the excess may run off into drains.
Is this lawn fertilizer calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.