🧪 Fertilizer Dilution Calculator

Scale your fertilizer's label instructions (like '1 tsp per gallon') to whatever container size you're actually using. Always follow your product's own label ratio — this just does the scaling math.

Label amount

Unit

Per this many gallons

Your container size (gallons)

How the label ratio is rescaled

The tool keeps the concentration on your bottle constant and works out the dose for the container you are actually filling:

dose = (label amount ÷ label volume) × your container volume

A label reading 1 tsp per gallon with a half-gallon watering can gives 0.50 tsp. A label reading 0.5 tsp per 2 gallons, poured into a 1.5 gallon can, gives (0.5 ÷ 2) × 1.5 = 0.38 tsp after rounding. Both volume boxes are read as US gallons and the answer is rounded to two decimals.

Reading your bottle

No unit conversion happens. Choose tsp and the answer is in tsp; choose mL or pumps and it stays in those. Convert by hand if you need to: 1 tsp = 4.93 mL, 1 tbsp = 3 tsp = 14.79 mL, 1 US gallon = 3.785 L.
“Per this many gallons” is the label's figure, not yours. A 2 L metric label is 0.53 gallons.
Pumps only scale correctly if every pump delivers the same volume, so prime the bottle before you count.

The only authority on the rate is the product label in your hand. There is no universal dose per gallon: a 24-8-16 soluble powder and a 2-2-2 fish emulsion differ by more than a hundredfold in strength. Half-strength feeding in low light or over winter is a common grower judgement, not something this arithmetic can decide for you. Salt crust on the soil and browning leaf tips mean you have gone too far.

Frequently asked questions

How much fertilizer for a 2 litre watering can?

Two litres is 0.53 gallons, so enter that as your container size. At a label rate of 1 tsp per gallon you would use 0.53 tsp.

My label says teaspoons but I only have a tablespoon — what do I do?

The tool will not convert for you. Work the answer out in teaspoons, then divide by 3, because 1 tbsp = 3 tsp. A result of 4.5 tsp is 1.5 tbsp.

Should I keep feeding houseplants through winter?

Most growers cut back or stop while light is short and growth has stalled, since unused salts build up in the pot. Plants under grow lights on a long daily cycle may still be growing and still be feeding.