Everyday
Lawn Fertilizer Calculator
Pick your grass type, enter your lawn size and bag details, and get a full-year nitrogen schedule: how much to apply each month, how many bags to buy, and what it costs.
How it works
Behind the numbers
Fertilizer bags list three numbers, N-P-K, and only the first one matters for dosing nitrogen. A 20-0-0 bag is 20% nitrogen by weight, so delivering 1 lb of nitrogen takes 5 lb of product. The calculator does that division for every application, then rounds up to whole bags.
Timing follows the Virginia DCR fertilizer table: cool-season grasses get most of their nitrogen in September through November, warm-season grasses from April through August. Your annual target is split across those months in proportion to the table's recommended rates.
Purdue Extension caps a single application at 1.0 lb of nitrogen per 1,000 sq ft for quick-release fertilizer, or 2.0 lb when more than half the nitrogen is slow-release. Any month above the cap is automatically split into two visits at least four weeks apart, which is how you feed the lawn without burning it.
FAQ
Questions, answered
How much fertilizer does my lawn need per year?
Virginia DCR recommends 2–3.5 lb of nitrogen per 1,000 sq ft per year for bluegrass, tall fescue, and ryegrass, and 2–4 lb for bermudagrass and St. Augustine. Low-input grasses like fine fescue, zoysia, and centipede need only 1–2 lb. Convert nitrogen to product by dividing by the bag's N%: at 20% N, 3 lb of nitrogen means 15 lb of product per 1,000 sq ft.
How much nitrogen can I apply at once without burning the lawn?
Purdue Extension advises no more than 1.0 lb of actual nitrogen per 1,000 sq ft in a single application with quick-release fertilizer. If more than half the nitrogen is slow-release, you can go up to 2.0 lb. Higher rates should be split into applications at least four weeks apart.
When should I fertilize cool-season grass?
Fall is the main season: September through early November, per the Virginia DCR table, with an optional light May application. Avoid fertilizing dormant or drought-stressed turf, and skip summer applications on cool-season lawns.
What do the three numbers on a fertilizer bag mean?
They are the N-P-K analysis: the percentages of nitrogen, phosphorus, and potassium by weight. A 20-0-0 bag is 20% nitrogen with no phosphorus or potassium. Only nitrogen drives the application rate for most lawns; add phosphorus or potassium only if a soil test says you need them.