Enter your lawn's square footage and the bag's first number — get pounds to spread, in spreader-load terms.
Water it in after spreading (a quarter inch), keep granules off driveways and out of storm drains, and never exceed 1 lb N per 1,000 sq ft in one application.
The fertilizer math
lbs of product per 1,000 sq ft = desired lb N ÷ (bag's N% ÷ 100)
total = that × (your sq ft ÷ 1,000)
This is the formula every extension service publishes and every bag obscures: the bag is mostly filler carrying its N percentage, so a 24% bag needs about 3 lbs of product to deliver 0.75 lbs of nitrogen. Higher-N bags need less product for the same feeding — which is why comparing bags by price-per-pound-of-bag misleads; price per pound of NITROGEN is the real cost.
A worked example
A 5,000 sq ft lawn, a 50-lb bag of 24-0-4, standard 0.75 lb feeding: 3.1 lbs of product per 1,000 → about 15.6 lbs total — roughly a third of the bag, which at this rate covers ~16,000 sq ft, three full feedings of this lawn. The bag's own "covers 12,500 sq ft" claim assumes the full 1.0 lb rate.
Getting it onto the lawn evenly
Weigh out the total (a bathroom scale and a bucket work), spread half in one direction and half perpendicular, and water it in. Feed cool-season lawns mainly in fall and spring, warm-season in late spring through summer. Your square footage comes from thelawn size calculator, and seeding plans pair with thegrass seed calculator — starter fertilizer and seed go down the same week.
Frequently asked questions
What do the three numbers on a fertilizer bag mean?
N-P-K: the percentage by weight of nitrogen (grows green blades), phosphorus (roots — often 0 in lawn ferts, it's restricted in many states), and potassium (stress tolerance). A 24-0-4 bag is 24% nitrogen, so a 50-lb bag contains 12 lbs of actual nitrogen. Every lawn dose starts from that percentage.
How much nitrogen should a lawn get?
The near-universal rule: 0.75 to 1.0 lb of actual nitrogen per 1,000 sq ft per application, and no more than 1 lb in one shot — more than that risks burning the grass and feeds disease. Seasonal total runs 2–4 lbs per 1,000 depending on grass type and how green you want to be.
How do I set my spreader?
Bag settings are starting points, not gospel — spreaders drift with age and walking speed. The self-calibrating trick: put HALF the calculated fertilizer in the spreader at a lower setting, cover the whole lawn, then spread the second half walking the perpendicular direction. Perfect coverage, no striping, impossible to badly overdose.
Slow release vs fast release fertilizer?
The label says it near the N number ('slow release' / '% slowly available'). Fast release greens up in days but burns easier and fades in weeks — respect the 1 lb limit strictly. Slow release feeds for 6–10 weeks and forgives error — the beginner-friendly choice, usually worth the few extra dollars.