Fertilizer Rate Calculator
Enter the N-P-K on any bag and your lawn size. Get pounds per 1,000 sq ft, total pounds for the lawn, how many bags to buy, and the actual nutrients delivered.
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1 minuteFertilizer rates, explained
Every fertilizer rate comes down to one conversion: the bag's nitrogen percentage into pounds of actual nitrogen on the ground.
Lawn fertilizer recommendations are written in pounds of actual nitrogen per 1,000 sq ft, but bags are sold by product weight. The bridge is the first number in the N-P-K analysis: it's the percent nitrogen by weight. To hit 1 lb of nitrogen per 1,000 sq ft with a 16-4-8, divide 1 by 0.16 and you get 6.3 lbs of product per 1,000 sq ft.
That's why the same target rate needs wildly different amounts of product: 10 lbs of 10-10-10, 6.3 lbs of 16-4-8, but only 2.2 lbs of 46-0-0 urea. Higher-analysis bags cover more lawn per pound, which usually makes them cheaper per feeding even at a higher sticker price.
Balanced numbers look appealing on the shelf, but established lawns rarely need equal parts of everything.
- 16-4-8 (a 4-1-2 ratio): the classic turf ratio. Matches how grass actually consumes nutrients and suits most established lawns.
- 32-0-4 and other phosphorus-free blends: the default for lawns that don't have a soil-test-confirmed phosphorus deficiency. Several states restrict phosphorus on established turf.
- 10-10-10 / 13-13-13 / 19-19-19: balanced garden fertilizers. Fine in a pinch and good for new seedings where phosphorus helps root establishment.
- 46-0-0 urea: pure fast nitrogen. Cheap and effective but easy to burn with — apply at low rates and water in promptly.
When in doubt, run a soil test. It replaces guesswork with numbers: if phosphorus and potassium are already adequate, all you're really shopping for is nitrogen, and the cheapest source per pound of N wins.
The calculator gives you the right amount. Spreader technique is what actually delivers it evenly.
Spreader setting charts on the bag are starting points, not gospel — walking speed, spreader wear, and granule size all change the effective rate. The reliable method: weigh out the total product your lawn needs, set the spreader to half the bag's recommended setting, and make two full passes at right angles to each other. You'll run out of product right as you finish the second pass if the setting is right.
Water the lawn after granular feeding unless the bag says otherwise. A quarter inch of irrigation moves the granules off the leaf blades and starts releasing nutrients into the root zone, which is also your insurance against burn on hot days.
How much fertilizer do I apply per 1,000 sq ft?
Divide your target nitrogen rate by the bag's nitrogen percentage. At the standard 1 lb of nitrogen per 1,000 sq ft, a 10-10-10 bag needs 10 lbs of product per 1,000 sq ft, a 16-4-8 needs about 6.3 lbs, and 46-0-0 urea needs about 2.2 lbs. The first number in the N-P-K analysis is the percent nitrogen by weight.
What do the three numbers on a fertilizer bag mean?
The N-P-K analysis is the percent by weight of nitrogen (N), phosphate (P2O5), and potash (K2O). A 50 lb bag of 16-4-8 contains 8 lbs of nitrogen, 2 lbs of phosphate, and 4 lbs of potash. The rest is carrier material that helps spread the nutrients evenly.
How much nitrogen should my lawn get per application?
Most lawns do best with 0.5 to 1 lb of actual nitrogen per 1,000 sq ft per application. Use the lighter end (0.5 to 0.75 lb) for slow-release feedings, cool-season lawns in summer, or sandy soils, and up to 1 lb for the main spring and fall feedings. Rates above 1 lb in a single application risk burn and surge growth.
How many bags of fertilizer do I need?
Multiply your per-1,000 sq ft rate by your lawn size in thousands of square feet, then divide by the bag weight and round up. Example: 6.3 lbs per 1,000 sq ft on an 8,000 sq ft lawn is about 50 lbs of product, exactly one 50 lb bag of 16-4-8.
Can I use 10-10-10 on my lawn?
Yes, balanced 10-10-10 works for lawns, but most established lawns don't need that much phosphorus, and some states restrict phosphorus applications unless a soil test shows a deficiency. A turf-formulated ratio like 16-4-8 or a phosphorus-free 32-0-4 usually matches lawn needs better. Run a soil test before adding phosphorus.
What happens if I apply too much fertilizer?
Over-application causes fertilizer burn (yellow or brown streaks where nitrogen salts dried out the grass), surge growth that stresses the plant, and runoff that wastes money. If you over-apply, water deeply right away to dilute the salts, and skip the next scheduled feeding. Applying at half rate in two perpendicular passes is the easiest way to avoid striping and overlap errors.