Nutrient (N-P-K) calculator
The three numbers on a fertiliser bag are percentages by weight. This turns them into the pounds of nitrogen, phosphate and potash you are actually putting on the grass.
What lands on the grass
| Nutrient | Per 1,000 ft² | Total, 5,000 ft² |
|---|---|---|
| Nitrogen (N) | 0.96 lb | 4.8 lb |
| Phosphate (P₂O₅) | 0.08 lb | 0.4 lb |
| Potash (K₂O) | 0.44 lb | 2.2 lb |
Reading the bag
A 24-2-11 bag is 24% nitrogen, 2% phosphate and 11% potash by weight; the rest is carrier and filler. Spread four pounds of it per thousand square feet and you have applied 0.96 lb of nitrogen, 0.08 lb of phosphate and 0.44 lb of potash to that thousand square feet.
The nitrogen number is the one that drives growth and the one to budget across a season. The other two are worth checking against a soil test rather than applied by habit — phosphate in particular is restricted in some places unless a test shows a need.