Fertilizer Ratio Calculator
Area
Rate is for
Lawns: 0.5–1 lb of nitrogen per 1,000 ft² per feeding
Fertilizer to apply
20.8 lb
4.17 lb per 1,000 ft² · 0.42 bags of 50 lb
A 24-0-11 fertilizer is 24% nitrogen (N) by weight, so supplying 1 lb of nitrogen (N) takes 1 ÷ 0.24 = 4.17 lb of product per 1,000 ft².
Nutrients applied
- Nitrogen (N)
- 5 lb
- Phosphate (P₂O₅)
- 0 lb
- = 0 lb P
- Potash (K₂O)
- 2.29 lb
- = 1.9 lb K
- N : P₂O₅ : K₂O
- 24 : 0 : 11
Bag grades list phosphorus as P₂O₅ and potassium as K₂O, not the elements; multiply by 0.436 and 0.830 to convert. The other 65% of the bag is carrier, filler and secondary nutrients.
Work out how much of a fertilizer to spread to deliver a target rate of nitrogen, phosphate or potash per 1,000 square feet or per acre, from the three numbers on the bag, with the nutrients it supplies and the number of bags.
Formula
Worked Example
The bag is 24% nitrogen, so 1 lb of N takes 1 ÷ 0.24 = 4.17 lb of product per 1,000 ft². The lawn needs 5 lb of nitrogen in all, or 20.8 lb of fertilizer, which also delivers 2.29 lb of potash.
Frequently Asked Questions
What do the three numbers on a fertilizer bag mean?
The percentages by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O). A 50 lb bag of 24-0-11 contains 12 lb of nitrogen, no phosphate and 5.5 lb of potash; the rest is carrier and other nutrients.
How much nitrogen does a lawn need?
Typically 0.5–1 lb of nitrogen per 1,000 ft² per feeding, and 2–4 lb a year for cool-season grasses depending on how they are used and whether clippings are left on the lawn. Many areas restrict phosphorus on lawns unless a soil test shows a need.
Why are phosphorus and potassium given as P₂O₅ and K₂O?
It is a labeling convention from older chemical analysis. To get the elemental amounts multiply by 0.436 for phosphorus and 0.830 for potassium; a 10-10-10 fertilizer is really 10% N, 4.4% P and 8.3% K.