HowMuchIt

HowMuchIt / Fertilizer

How much fertilizer do I need?

The first number on the bag is the percent of nitrogen. Divide 100 by it and you get the pounds of product that put 1 pound of nitrogen on 1,000 square feet; the calculator scales it to your lawn.

Rule card for Fertilizer: N-P-K = percent by weight; Lb per 1,000 sq ft = 100 / N; At most 1 lb of N at a time.
N-P-K = percent by weight.

Work out your fertilizer

Pounds of product per 1,000 sq ft for 1 lb of nitrogen = 100 / the first number: 6.25 lb of a 16-4-8. Never more than 1 lb of nitrogen per 1,000 sq ft at one time. The spreader setting is printed on the bag.

Reading the bag

The three numbers, N-P-K, are the percent by weight of nitrogen, phosphate and potash. A 50 pound bag of 10-6-4 holds 5 pounds of nitrogen. A typical single feeding is up to 1 pound of nitrogen per 1,000 square feet, and never more than that at one time. The spreader setting for each spreader model is printed on the bag; if yours is not listed, calibrate it over a measured area.

Keep it on the lawn

Do not fertilize when heavy rain is coming: it washes off as runoff. Sweep anything that lands on the driveway or sidewalk back onto the grass, and keep a broadcast spreader away from water, roads and pavement.

Questions people ask

How much 16-4-8 for 5,000 sq ft?

6.25 lb per 1,000 sq ft: about 31 pounds for one feeding.

What do the three numbers mean?

Percent of nitrogen, phosphate and potash, by weight.

Good to know

  • The three numbers on a fertilizer bag (N-P-K) are the percent by weight of nitrogen, phosphate and potash; a 50 lb bag of 10-6-4 holds 5 lb of nitrogen.1,2,3
  • Pounds of product per 1,000 sq ft to apply 1 lb of nitrogen = 100 divided by the first number on the bag (for 16-4-8: 100 / 16 = 6.25 lb).1,3,4
  • A typical single feeding is up to 1 lb of nitrogen per 1,000 sq ft; never apply more than 1 lb of nitrogen per 1,000 sq ft at one time.2,3,5,6
  • Do not fertilize when heavy rain is expected; it can wash the fertilizer away as runoff.2,6,7
  • Sweep any fertilizer that lands on a driveway or sidewalk back onto the lawn right away.2,6,7
  • Keep rotary (broadcast) spreaders away from water and from roads, driveways and sidewalks.2,7
  • The spreader setting for each spreader model is printed on the fertilizer bag; use that number.8,9
  • If your spreader is not listed on the bag, calibrate it: spread a known amount over a measured area and adjust the dial until it matches the label rate.7,8,9

How we checked this page

Checked on October 27, 2026. We kept a fact only when two independent publishers agree, and each one is numbered to its sources below. Where sources give different numbers, we keep only what they share. We never write a price. This page was written with an AI assistant and checked against the sources below.

Sources

  1. Extension Gardener Handbook, 9. Lawns, NC State Extension
  2. Getting the most out of your lawn soil test report, Cornell University CALS, School of Integrative Plant Science, Horticulture Section
  3. Fertilizing Lawns (HGIC 1201), Clemson Cooperative Extension, Home and Garden Information Center
  4. Calculations Used to Determine the Amount of Fertilizer Needed to Treat Turf, Penn State Extension
  5. Suggested Fertilizer Practices for Lawns (Dawn Pettinelli), UConn Soil Nutrient Analysis Laboratory
  6. Caring for Your Lawn and the Environment (AG-597), NC State Extension
  7. Healthy Lawns, Clean Water: fertilizer application, Suffolk County, NY, Division of Water Quality Improvement (local government)
  8. How to Calibrate a Spreader and Find the Right Settings, ScottsMiracle-Gro
  9. How to Use a Broadcast Spreader, The Good Earth Garden Center (Little Rock, AR)
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