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Fertilizer Calculator

Calculate how much fertilizer to apply based on lawn or garden area and N-P-K ratio. Get exact grams or pounds for any fertilizer product.

sq ft

Select a common ratio or enter custom values from your fertilizer bag

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%
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Selected: 1.0 lb nitrogen per 1,000 sq ft

Fertilizer Needed

Total Amount
0 lbs
0 kg
Grams
0
g
Cups (approx)
0
~200g/cup
0 lbs per 1,000 sq ft | 0 kg per 100 m²

Actual Nutrients Applied

Nitrogen (N)
0
lbs
Phosphorus (P₂O₅)
0
lbs
Potassium (K₂O)
0
lbs

Application tips:

  • Never apply more than 1.5 lbs N per 1,000 sq ft in a single application
  • Water thoroughly after applying to prevent burn and help absorption
  • Apply when rain is expected, or water in within 24 hours
  • Use a broadcast spreader for even coverage on lawns

About This Tool

Applying the right amount of fertilizer is crucial — too little and your plants starve, too much and you risk burning them, wasting money, and polluting groundwater. This calculator takes the guesswork out by computing exactly how much of your specific fertilizer product to apply based on area and desired nitrogen rate. Enter your lawn or garden size, select your fertilizer's N-P-K ratio (the three numbers on the bag like 10-10-10 or 20-5-10), and choose your target application rate. The calculator shows how many grams, pounds, or cups of fertilizer you need for the entire area. It also breaks down the actual pounds of nitrogen, phosphorus, and potassium you'll be applying. Works for lawns, vegetable gardens, flower beds, and container plants. Supports both metric (m²) and imperial (sq ft) measurements. Common presets for lawn maintenance, new seeding, and heavy feeding scenarios are included.

How to Use

1. Enter your lawn or garden area in square feet or square meters 2. Select or enter your fertilizer's N-P-K ratio (check the bag) 3. Choose the desired nitrogen application rate (lbs N per 1000 sq ft) 4. See the total fertilizer amount needed in multiple units 5. View the breakdown of actual N, P, K being applied 6. Use "Copy Link" to save your calculation for future reference

Formula

Fertilizer Amount = (Area × Desired N Rate) ÷ (N% ÷ 100) Example: 5,000 sq ft lawn, 10-10-10 fertilizer, 1 lb N per 1,000 sq ft - Desired N = 5,000 ÷ 1,000 × 1 = 5 lbs nitrogen - Fertilizer needed = 5 ÷ 0.10 = 50 lbs of 10-10-10 Nutrient breakdown: - Actual N = Fertilizer lbs × N% - Actual P₂O₅ = Fertilizer lbs × P% - Actual K₂O = Fertilizer lbs × K% Unit conversions: - 1 lb = 453.6 g - 1 sq ft = 0.0929 m² - 1 cup granular fertilizer ≈ 200g (varies by product)

Frequently Asked Questions

What do the N-P-K numbers mean?
N-P-K represents the percentage by weight of nitrogen (N), phosphorus (P₂O₅), and potassium (K₂O) in the fertilizer. A 10-10-10 fertilizer is 10% nitrogen, 10% phosphorus, and 10% potassium — the remaining 70% is filler and micronutrients. A 20-5-10 has twice the nitrogen concentration, so you need half as much product to apply the same amount of N.
How much fertilizer do I need per 1000 sq ft?
It depends on the fertilizer's N-P-K ratio and your desired application rate. For lawn maintenance, 1 lb of nitrogen per 1,000 sq ft is typical. With 10-10-10 fertilizer, that's 10 lbs of product. With 20-10-10, it's only 5 lbs. This calculator does the math for any ratio.
What is the best N-P-K ratio for lawns?
For established lawns, a high-nitrogen fertilizer like 20-5-10 or 30-0-4 promotes green growth. For new lawns or fall applications, balanced fertilizers like 10-10-10 help root development. Phosphorus (the middle number) is most important during establishment; nitrogen (first number) for ongoing maintenance.
How often should I fertilize my lawn?
Cool-season grasses (fescue, bluegrass): fertilize in early fall and late spring, 2-4 times per year. Warm-season grasses (bermuda, zoysia): fertilize in late spring through summer, 3-5 times per year. Never apply more than 1 lb nitrogen per 1,000 sq ft in a single application to avoid burning.
Can I use this calculator for vegetable gardens?
Yes. Vegetable gardens typically need 2-3 lbs nitrogen per 1,000 sq ft per growing season, split into multiple applications. Use a balanced fertilizer like 10-10-10 at planting, then side-dress with nitrogen-heavy fertilizer during the growing season. Always follow soil test recommendations when available.
What happens if I apply too much fertilizer?
Over-fertilizing causes 'fertilizer burn' — brown, dead patches from salt damage to roots. It also wastes money and pollutes waterways through runoff. Excess nitrogen promotes leafy growth at the expense of flowers and fruit. If you over-apply, water heavily to dilute the fertilizer and flush it through the soil.
How do I convert fertilizer amounts between units?
1 pound = 453.6 grams = about 2.25 cups (for granular fertilizer). 1 kg = 2.2 lbs. For area: 1,000 sq ft = 93 m². This calculator shows results in multiple units so you can use whatever measuring tool you have.

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