Fertilizer Calculator
5 free tools to help you fertilize correctly. Start with the dosage calculator below, or pick another tool.
How Much Fertilizer Should I Apply?
What are you fertilizing? Pick from 150+ plants.
Size of your lawn or garden bed
The 3 numbers on the bag (e.g. 10-10-10)
How Does the Dosage Formula Work?
The calculator uses: Pounds of product = (Desired N per 1,000 sq ft / Fertilizer N%) x (Area / 1,000)
For example, if your tomatoes need 1 lb N per 1,000 sq ft with a 10-10-10 fertilizer on 500 sq ft: (1 / 0.10) x (500 / 1000) = 5 pounds needed.
What NPK Ratio Should You Choose?
The best NPK ratio depends on your plant type and growth stage. Browse our plant guides for specific recommendations, or read our NPK ratios explained guide.
What is Burn Risk?
Fertilizer burn occurs when too much nitrogen is applied. The calculator flags applications above 1 lb N per 1,000 sq ft as medium risk, above 1.5 lbs as high risk. Read more about burn prevention.