Fertilizer calculator
Enter your bed size, pick what you're feeding and which fertilizer you have. You'll get the pounds of product to apply and the nutrients it delivers.
How this is calculated
Fertilizer rates are set by actual nitrogen, not product weight. Target nitrogen (lb) = area ÷ 1,000 × the rate for that crop (0.5 lb/1,000 sq ft for light feeders, 1.0 for most vegetables and new lawns, 1.5 for heavy feeders like corn and brassicas).
Product needed (lb) = target nitrogen ÷ (N% ÷ 100). A 10-10-10 fertilizer is 10% nitrogen, so 0.4 lb of actual N needs 4 lb of product. Phosphate and potash delivered are the P and K percentages of that product weight. “Cups” assumes about half a pound of dry granular fertilizer per cup — always check your bag.
Split the total into two or three feedings over the season rather than applying it all at once, and water it in.
Common questions
What does the N-P-K on a fertilizer bag mean?
The three numbers are the percentage by weight of nitrogen (N), phosphate (P2O5) and potash (K2O) in the bag. A 10-10-10 bag is 10% each; the rest is filler.
Should every crop in a bed get the same rate?
No - heavy feeders (corn, squash, brassicas, tomatoes) want roughly 1.5x the nitrogen of light feeders (beans, peas, herbs, most root crops), since legumes fix their own nitrogen and many roots and herbs go leafy or bolt if overfed.
Can I use this for a lawn instead of a garden bed?
Yes - enter your lawn area and use a light-to-medium feeder rate (around 1 lb N per 1,000 sq ft per feeding is typical for an established lawn); see the grass seed calculator for seeding a new one.