Fertilizer Calculator
This fertilizer calculator shows how much fertilizer your area needs: enter square feet or meters, the wanted rate and the N-P-K numbers on the bag, then read the amount per area and in total.
Example: Area 100 m² · Leading nutrient: Nitrogen (N) · Wanted rate 5 g nutrient per m² · Nitrogen (N) in the fertilizer 12 % · Phosphate (P₂O₅) in the fertilizer 6 % · Potash (K₂O) in the fertilizer 6 % · Bag size 5 kg → Fertilizer needed: 4.2 kg of fertilizer for 100 m² (42 g per m²). Source: Wikipedia – NPK rating (stating N, P₂O₅ and K₂O as mass percent on fertilizer packaging). Updated: .
How it is calculated
For 100 m² (about 1,076 sq ft), a wanted rate of 5 g nitrogen per m² and a fertilizer with 12 % N you need about 4.2 kg (9.2 lb) of fertilizer. The calculator derives the amount from the nutrient content on the bag and also shows how much phosphate and potash come with it.
How it is calculated
The product amount per square meter is the wanted nutrient rate divided by the nutrient content as a decimal: 5 g ÷ 0.12 gives 41.7 g of fertilizer per m². Times the area gives the total. The other percentages of the N-P-K rating show how much phosphate and potash you apply at the same time. The rate itself is a value you set: it depends on plant type, soil and fertilizer form.
Tips for use
- Calculate with the nutrient that matters most for your plants, usually nitrogen for lawns and many vegetables.
- Split large amounts into several applications instead of applying everything at once.
- Spread evenly: a scale and a spreader help to keep to the amount per m².
Related calculators: raised bed, plant spacing and the area converter.
Frequently asked questions
How much fertilizer do I need per square meter?
Divide the wanted nutrient rate in grams by the nutrient content as a decimal. For 5 g of nitrogen at 12 % N that is about 42 g of fertilizer per m².
What does 12-6-6 on the bag mean?
The numbers are percent by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O). 100 g of fertilizer then contain 12 g N, 6 g P₂O₅ and 6 g K₂O.
How do I know the right rate?
The rate depends on plant, soil and fertilizer type. Use the label recommendation, a soil test or an adviser and enter the value in the calculator.
Can I fertilize too much?
Yes, too much fertilizer stresses plants and soil and can reach groundwater. Stick to the recommended rate and the rules that apply to you.
Sources and legal basis
As of: · Editorial policy
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