A liquid fertilizer calculator for mixing, ppm and tank dilution
Fertilizer labels say things like “5 ml per litre”, “1 tablespoon per gallon” or “feed at 150 ppm N”, but your watering can, knapsack sprayer or drip tank is a different size. This liquid fertilizer calculator turns any of those instructions into the exact amount of product to measure: millilitres of a liquid concentrate or grams of a water-soluble powder for your tank, in litres or gallons.
It works four ways: from a label rate, from a target ppm of nitrogen, phosphate or potash for fertigation and hydroponics, from a percent solution for foliar sprays, and from a rate per hectare or acre split into sprayer tanks. Every answer also shows the ppm of N, P₂O₅ and K₂O the plants receive — an NPK dilution calculator in one — and handles 1:100-style injectors. Nothing is uploaded.
How to use the Liquid Fertilizer Calculator
- Choose Label rate, Target ppm, % solution or Per hectare / acre.
- Enter the product: liquid or water-soluble powder, its N, P₂O₅ and K₂O percentages, and for a liquid its density from the label or safety data sheet.
- Enter the rate: the label dose, the ppm you want, the spray strength, or the nutrient rate with field area and spray volume.
- Enter the water in your tank and, if you use an injector or doser, its ratio (1:100 means 1 part stock to 100 parts water).
- Read the amount to add, the ppm it gives and the table for other tank sizes, then copy the result.
Liquid Fertilizer Calculator features
Four ways to dose
Label rate, target ppm, percent solution and field rate per hectare or acre in one tool.
Liquids by weight
N-P-K on a liquid label is by weight; density (kg/L or lb/gal) converts it into mg of nutrient per ml.
Metric and US units
Litres, millilitres, US and UK gallons, teaspoons, tablespoons, fluid ounces and cups; grams, kilograms, ounces and pounds.
Injector stock tanks
With a 1:R injector the stock is R times stronger; the calculator gives the stock recipe and the final ppm.
Tank-size table
The same dose for 1 L to 1,000 L or 1 to 100 gallons, ready to print or copy.
How the dilution is calculated
One ppm in water is one milligram per litre. A water-soluble powder with 20% N carries 200 mg of N per gram. A liquid label also gives percent by weight, so multiply by its density: a 10-10-10 liquid weighing 1.25 kg per litre carries 1.25 × 10 × 10 = 125 mg of N per ml. Then product per litre = target ppm ÷ mg of nutrient per ml (or g), and the tank amount is that times the litres of water.
Worked example (powder): 200 ppm N from a 20-20-20 in 100 US gallons (378.5 L) needs 200 × 378.5 ÷ 200 = 378.5 g, about 13⅓ oz. That matches the classic US rule ounces per 100 gallons = ppm ÷ (%N × 0.75) used in UMass Extension’s greenhouse fertilizer fact sheet.
Worked example (liquid): a label rate of 5 ml per litre in a 16 L knapsack sprayer is 80 ml, and with a 10-10-10 at 1.25 kg/L the spray holds 625 ppm each of N, P₂O₅ and K₂O.
Injectors, percent solutions and field rates
A 1% injector setting is a 1:100 ratio and 2% is 1:50. The ratio says how strongly the stock is diluted — not the ppm the plants receive, which depends on how much fertilizer is in the stock. For dry fertilizers by the bag per acre, use the fertilizer calculator; to blend grades or convert ppm of water-soluble NPK, the NPK calculator; to set the spray volume, the sprayer calibration calculator.
| You know | Formula | Example |
|---|---|---|
| Injector 1:R | stock = final dose × R | 1:100 at 200 ppm N → stock tank at 20,000 ppm N |
| % v/v (liquid) | 1% = 10 ml per litre | 1% foliar spray in 15 L = 150 ml |
| % w/v (powder) | 1% = 10 g per litre | 0.5% in 10 L = 50 g |
| kg nutrient/ha | product/ha = kg × 1,000,000 ÷ mg per ml | 20 kg N/ha of a 32% N liquid at 1.32 kg/L ≈ 47.3 L/ha |
| lb/acre ↔ kg/ha | 1 lb/acre = 1.121 kg/ha | 10 lb N/acre = 11.2 kg N/ha |
Mixing tips
- Half-fill the tank with water, add the fertilizer while stirring, then top up to the mark.
- Keep calcium nitrate apart from phosphates and sulphates in concentrated stock tanks — they form insoluble deposits that block drippers.
- Check the final solution with an EC meter, subtracting the EC of your plain water.
- P and K ppm in hydroponic recipes are often elemental: P = P₂O₅ × 0.4364 and K = K₂O × 0.8301. The calculator shows both.
Liquid Fertilizer Calculator FAQ
How do I calculate liquid fertilizer per litre?
Multiply the label rate by your tank size: 5 ml per litre in a 16 L sprayer is 80 ml. If the label gives a rate per gallon, the calculator converts it. For a target ppm, divide the ppm by the mg of nutrient per ml (density × % × 10).
How many ml of fertilizer per gallon?
Use the label rate mode with “per 1 US gal”. One tablespoon is 14.8 ml, so 1 tbsp per gallon in a 2-gallon can is about 29.6 ml (1 fl oz).
What is an NPK dilution calculator?
It works out the ppm of N, P₂O₅ and K₂O after a fertilizer is diluted in water, or the amount needed for a target ppm. This calculator does both for liquids and powders.
How do I set a 1:100 fertilizer injector?
Make the stock 100 times stronger than the solution you want at the plants. For 200 ppm N from a 20% N powder, dissolve 100 g per litre of stock (100 × 1 g per litre).
Why does the liquid density matter?
Liquid fertilizer percentages are by weight. A litre of a dense liquid weighs more than a kilogram, so it carries more nutrient per ml than its label percentage alone suggests.
Is the result safe for my plants?
It is arithmetic, not a recommendation. Follow the product label and local agronomy advice for your crop and growth stage, and test on a few plants first when spraying leaves.