Fertilizer Ratio Calculator
Calculate fertilizer needs based on NPK ratio, garden area, and application rate. Find out how many bags you need and the cost.
Inputs
Results
Total Fertilizer Needed
10 lbs
≈ 2 bags of sugar
How to Use This Calculator
- Read the NPK label on your fertilizer bag and enter the three numbers into the N%, P%, and K% fields.
- Enter your total garden area in square feet and the desired application rate (lbs of nitrogen per 1,000 sq ft — typically 1 lb for lawns).
- Input the bag weight in pounds and cost per bag so the calculator can estimate the number of bags and total cost.
- Review Total Fertilizer Needed (lbs) and Bags Needed to plan your purchase.
- Check the individual nutrient delivery weights (N, P, K in lbs) to verify you are meeting your soil's nutritional goals.
How the result changes with Nitrogen (N)
| Nitrogen (N) | Total Fertilizer Needed |
|---|---|
| 5 | 20 lbs |
| 18 | 5.56 lbs |
| 33 | 3.03 lbs |
| 45 | 2.22 lbs |
What each input means
- Nitrogen (N)
- Nitrogen percentage from the fertilizer label (first number in NPK).
- Phosphorus (P)
- Phosphorus percentage from the fertilizer label (second number in NPK).
- Potassium (K)
- Potassium percentage from the fertilizer label (third number in NPK).
- Garden Area
- Total area to fertilize in square feet.
- Application Rate
- Pounds of nitrogen to apply per 1000 sq ft. Typical lawn rate is 1 lb.
- Bag Weight
- Weight of each fertilizer bag in pounds.
- Cost per Bag
- Price per bag of fertilizer.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersNitrogen (N) = 10, Phosphorus (P) = 10, Potassium (K) = 10, Garden Area = 1000 = 7 input(s) provided
- Calculate Total Fertilizer NeededTotal Fertilizer Needed10 = 10
- Calculate NPK RatioNPK Ratio = `${nRatio10-10-10 = 10-10-10
- Calculate Nitrogen (N) DeliveredNitrogen (N) Delivered1 = 1
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