Turf: Lawn Care Calculator
The lawn-care calculator that doesn't sell you fertilizer — just the math, every number cited.
What it does
Most "lawn apps" are a funnel for one brand's products. Turf is a neutral, citation-backed tool that just does the math: how much nitrogen, how much seed, how much lime, what spreader setting, what dilution. The hero nitrogen-rate calculator is free forever at full citation quality — enter your bag's N-P-K, target rate, and lawn size, and get product per 1,000 sq ft, bags needed, and a hard guardrail at the ~1.0 lb N per 1,000 sq ft single-application cap (Purdue, Virginia Cooperative Extension).
A one-time $4.99 Turf Pro purchase unlocks five more calculators — spreader calibration (weigh-back method), liquid dilution / tank-mix, lime & sulfur pH amendment by soil texture, grass seed rate by species, and PGR growing-degree-day timing on the Kreuser & Soldat model. No subscription, no ads, no account, works offline.
Turf is honest by design: it shows its work and flags what's disputed — where a popular lime table isn't in any primary extension publication, or where a GDD target is validated for putting greens rather than home lawns, Turf says so plainly. Sources include Purdue Turfgrass, Penn State Extension, Michigan State, University of Minnesota, NC State, Cornell, Texas A&M AgriLife, Clemson HGIC, and the US EPA. For any pesticide or plant-growth regulator, the label is the law.
Common questions
How much fertilizer does my lawn actually need? That's the exact question the free calculator answers. Lawn fertilizer directions are written per bag, but university turf programs work in pounds of nitrogen per 1,000 sq ft — so Turf converts: enter the N-P-K off your bag, your target rate, and your lawn size, and it returns how much product to spread and how many bags to buy. The guardrail matters as much as the math: staying at or under ~1.0 lb of nitrogen per 1,000 sq ft in a single application is the widely cited extension cap that keeps you from burning the lawn or feeding the storm drain instead of the grass.
Why does a calculator beat the bag's spreader setting? Because the bag doesn't know your spreader's wear, your walking speed, or your actual lawn size — the printed setting is a factory guess. The math route (and, in Pro, the weigh-back calibration method) replaces that guess with your own numbers.
What's free and what's paid? The nitrogen-rate calculator is free forever at full citation quality. A one-time $4.99 unlocks the other five calculators — spreader calibration, liquid dilution, lime & sulfur by soil texture, seed rate by species, and PGR timing. No subscription, no ads, no account, and everything works offline.
Can I trust the numbers? Every formula cites its source — Purdue, Penn State, Michigan State, Minnesota, NC State, Cornell, Texas A&M, Clemson — and where the sources disagree or a popular rule of thumb has no primary publication behind it, the app says so instead of pretending certainty. For pesticides and growth regulators, the label is always the law.