Calculate Fertilizer Needed
Enter your lawn details and fertilizer NPK ratio to find out exactly how much product to apply. Results update automatically.
Application Results
Nutrients Delivered Per 1,000 sq ft
| Detail | Value |
|---|
Seasonal Application Schedule
Based on your grass type selection.
Understanding NPK Ratios
Every fertilizer bag has three numbers separated by dashes -- the NPK ratio. These represent the percentage by weight of three essential nutrients:
| Nutrient | Symbol | What It Does | Signs of Deficiency |
|---|---|---|---|
| Nitrogen | N | Drives leaf and blade growth, gives grass its green color | Yellowing blades, slow growth, thin lawn |
| Phosphorus | P | Supports root development and seedling establishment | Poor root growth, slow establishment, dark purplish color |
| Potassium | K | Builds stress tolerance (drought, cold, disease) | Brown leaf edges, reduced drought tolerance, disease susceptibility |
Example: A 50 lb Bag of 20-5-10
- Nitrogen: 50 lbs x 20% = 10 lbs of actual nitrogen
- Phosphorus: 50 lbs x 5% = 2.5 lbs of actual phosphorus (as P2O5)
- Potassium: 50 lbs x 10% = 5 lbs of actual potassium (as K2O)
- Remaining 32.5 lbs: Filler, carrier material, and micronutrients
Grass Type Fertilizer Guide
Different grass species have different nutritional needs. Matching your fertilizer program to your grass type is the single most important factor in lawn health.
Cool-Season Grasses
These grasses grow most actively in spring and fall when temperatures are 60-75 degrees F. Primary fertilization should happen in fall.
| Grass Type | Annual N (lbs/1,000 sq ft) | Peak Feeding | Mowing Height |
|---|---|---|---|
| Kentucky Bluegrass | 2-4 | September-November | 2.5-3.5 in |
| Tall Fescue | 2-4 | September-November | 3-4 in |
| Perennial Ryegrass | 2-4 | September-October | 2-3 in |
| Fine Fescue | 1-2 | September-October | 2.5-3.5 in |
Warm-Season Grasses
These grasses thrive in summer heat (80-95 degrees F) and go dormant in winter. Fertilize during active growth from late spring through summer.
| Grass Type | Annual N (lbs/1,000 sq ft) | Peak Feeding | Mowing Height |
|---|---|---|---|
| Bermudagrass | 3-5 | May-August | 1-2 in |
| Zoysiagrass | 2-3 | May-July | 1-2.5 in |
| St. Augustinegrass | 2-4 | April-September | 3-4 in |
| Centipedegrass | 1-2 | May-June | 1.5-2.5 in |
| Bahiagrass | 2-3 | May-July | 3-4 in |
| Buffalograss | 0.5-2 | June-July | 2-3 in |
Common Fertilizer Products Reference
| Product Type | NPK | Best Use | Typical Cost |
|---|---|---|---|
| Scotts Turf Builder | 32-0-4 | General maintenance, quick green-up | $25-40 / 12,000 sq ft |
| Milorganite | 6-4-0 | Slow-release organic, safe on all grasses | $15-20 / 2,500 sq ft |
| Starter Fertilizer | 18-24-12 | New seed or sod establishment | $20-30 / 5,000 sq ft |
| Winterizer | 24-0-12 | Late fall, root energy storage | $25-35 / 10,000 sq ft |
| Balanced (General) | 10-10-10 | All-purpose, corrective feeding | $15-25 / 50 lb bag |
| Urea | 46-0-0 | Quick nitrogen boost (synthetic) | $25-40 / 50 lb bag |
| Weed & Feed | 28-0-3 | Fertilize + broadleaf weed control | $25-40 / 5,000 sq ft |
Prices are approximate U.S. retail as of 2025. Actual costs vary by region and retailer.
Spreader Settings Guide
Getting the right application rate depends on your spreader type and settings. Here are general guidelines:
Broadcast / Rotary Spreader
Best for large lawns. Throws product in a wide arc. Overlap passes by about 30% for even coverage.
Walk speed: Steady 3 mph pace
Pattern: Perimeter first, then parallel passes with overlap
Tip: Start with a lower setting and do two passes at right angles for more even coverage.
Drop Spreader
Most precise application. Product falls directly below. Good for small or irregularly shaped lawns.
Walk speed: Steady 3 mph pace
Pattern: Overlap wheel tracks slightly to avoid striping
Tip: Close the hopper before turning at row ends to avoid dumping product.
Handheld Spreader
Ideal for small areas under 2,000 sq ft. Crank-operated with adjustable rate.
Walk speed: Slow, steady pace
Pattern: Overlap each pass by half the spread width
Tip: Practice with sand first to understand the spread pattern.
Liquid Sprayer (Hose-End)
For liquid fertilizer concentrates. Attaches to garden hose for even spray coverage.
Walk speed: Slow sweep, 2-3 ft/second
Pattern: Overlap passes slightly. Apply until surface glistens.
Tip: Apply in early morning or evening to prevent leaf burn.
Calibrating Your Spreader
- Measure a 100 sq ft area on your driveway or sidewalk (e.g., 10 ft x 10 ft).
- Set your spreader to a mid-range setting.
- Weigh a small amount of fertilizer and load it.
- Apply to the 100 sq ft area at your normal walking pace.
- Weigh the remaining fertilizer. The difference is what you applied per 100 sq ft.
- Multiply by 10 to get the rate per 1,000 sq ft. Adjust the setting up or down as needed.
Fertilizer Application Tips
- Water after applying: Water your lawn lightly (about 0.25 inches) after granular fertilizer application to move nutrients into the soil and prevent leaf burn.
- Avoid fertilizing dormant grass: Do not fertilize warm-season grass in winter or cool-season grass during peak summer heat.
- Mow before fertilizing: Mow 1-2 days before application so the granules reach the soil surface more easily.
- Apply to dry foliage: Grass blades should be dry when you apply granular fertilizer, but the soil should be moist.
- Follow the 1 lb rule: Never apply more than 1 lb of nitrogen per 1,000 sq ft in a single application.
- Leave clippings: Grass clippings return about 1 lb of nitrogen per 1,000 sq ft per year. This can reduce your fertilizer needs by 25%.
- Get a soil test: Before starting a fertilizer program, get a soil test through your local university extension office (usually $15-25). It tells you exactly what your soil needs.
Frequently Asked Questions
How much fertilizer do I need per 1,000 sq ft?
It depends on the nitrogen percentage in your fertilizer. To deliver 1 lb of nitrogen per 1,000 sq ft, divide 100 by the nitrogen percentage. For a 20-5-10 fertilizer: 100 / 20 = 5 lbs of product per 1,000 sq ft. For a 10-10-10: 100 / 10 = 10 lbs of product per 1,000 sq ft.
What does NPK mean on fertilizer?
NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K) -- the three primary macronutrients that plants need. The three numbers on a fertilizer bag represent the percentage by weight of each nutrient. A 50 lb bag of 20-5-10 contains 10 lbs of nitrogen, 2.5 lbs of phosphorus (as P2O5), and 5 lbs of potassium (as K2O).
When should I fertilize my lawn?
For cool-season grasses (bluegrass, fescue, ryegrass): the most important application is in fall (September-November). A lighter spring application in April-May is optional. For warm-season grasses (Bermuda, Zoysia, St. Augustine): fertilize during active growth from late spring through summer (April-August). Never fertilize dormant grass.
Can I use too much fertilizer?
Yes. Over-fertilizing causes fertilizer burn (brown, dead patches), excessive top growth at the expense of roots, increased thatch buildup, greater susceptibility to disease, and nutrient runoff that pollutes waterways. Always follow recommended rates and never exceed 1 lb of nitrogen per 1,000 sq ft per application.
Should I use organic or synthetic fertilizer?
Both work. Synthetic fertilizers provide quick results and precise nutrient amounts. Organic fertilizers (like Milorganite) release nutrients slowly, improve soil biology, and are harder to over-apply. Many lawn care programs use a mix of both -- synthetic for targeted feeding and organic for soil health.
Does this calculator store my data?
No. All calculations run entirely in your browser. No data is sent to any server, and nothing is stored.
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Privacy & Limitations
- All calculations run entirely in your browser -- nothing is sent to any server.
- Results are estimates and may vary based on actual conditions.
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Lawn Fertilizer Calculator FAQ
How much fertilizer do I need per 1,000 sq ft?
Most lawns need 0.5 to 1.0 lb of nitrogen per 1,000 sq ft per application. The actual product amount depends on the fertilizer's NPK ratio. For example, a 20-5-10 fertilizer with 20% nitrogen requires 5 lbs of product to deliver 1 lb of nitrogen per 1,000 sq ft.
What does NPK mean on fertilizer?
NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K) -- the three primary plant nutrients. The numbers on a fertilizer bag (e.g., 20-5-10) represent the percentage by weight of each nutrient. A 50 lb bag of 20-5-10 contains 10 lbs nitrogen, 2.5 lbs phosphorus, and 5 lbs potassium.
When should I fertilize my lawn?
Cool-season grasses (Kentucky bluegrass, fescue, ryegrass) benefit most from fall fertilization (September-November) with a lighter spring application. Warm-season grasses (Bermuda, Zoysia, St. Augustine) should be fertilized primarily in late spring through summer (April-August) during active growth.
Can I use too much fertilizer?
Yes. Over-fertilizing can burn grass, cause excessive growth, increase thatch buildup, and pollute waterways through runoff. Always follow recommended application rates and never apply more than 1 lb of nitrogen per 1,000 sq ft in a single application.
Does this calculator store my data?
No. All calculations run entirely in your browser. No data is sent to any server, and nothing is stored.