Fertilizer NPK Calculator
Work out fertilizer from a target nitrogen rate. Enter your area, the pounds of nitrogen per 1000 square feet you want and the product's N percent.
How to calculate a fertilizer rate
- Enter the area you are feeding in square feet.
- Enter your target nitrogen in pounds per 1000 square feet.
- Enter the nitrogen percent, the first number on the NPK label.
Examples
20% N product, 1 lb N per 1000 over 5000 sq ft
Area 5000, target 1 lb N, 20% N
5 lbs of product per 1000 sq ft, 25 lbs total
Frequently asked questions
What do the NPK numbers mean?
NPK is the percent by weight of nitrogen, phosphorus and potassium. A 10-10-10 bag is 10 percent of each, so this calculator uses the first number, nitrogen, to set the rate.
How much nitrogen does a lawn need?
A common target is about one pound of nitrogen per 1000 square feet per feeding. Total yearly nitrogen varies by grass type, from two to four pounds across the season.
Why base the rate on nitrogen?
Nitrogen drives leaf growth and is the nutrient most often limiting, so lawn programs are set by the nitrogen rate. The other nutrients follow from the chosen product.
Can I split the application?
Yes. Applying half the rate twice, a few weeks apart, gives steadier growth and lowers the risk of burn. Never exceed the label's maximum single rate.
How do I avoid fertilizer burn?
Apply to a dry lawn, spread evenly and water it in afterward unless the label says otherwise. Slow-release nitrogen products are more forgiving than fast-release ones.
Related tools
Lawn Fertilizer Calculator
Find how many pounds of fertilizer to apply to hit a nitrogen rate. Enter the lawn area, target rate and the nitrogen percent on the bag to get the amount.
Grass Seed Calculator
Find how many pounds of grass seed your lawn needs. Enter the area and choose new lawn or overseeding to get the seed weight at the right rate.
Lawn Watering Calculator
Find how much to water your lawn. Enter area and inches per week to get gallons per week, plus sprinkler run time when you add gallons per minute.
Appliance Energy Calculator
Find what an appliance costs to run from its wattage. Enter watts, hours per day and your rate to see kWh and cost per day, month and year.
Aquarium Volume Calculator
Calculate your fish tank volume in gallons and liters from inside dimensions in inches. Set a fill level to estimate the actual water it holds.
Baseboard Calculator
Estimate linear feet and pieces of baseboard or trim for a room. Enter length and width, subtract doorways, set piece length and add waste.