Aquarium Medication Dosage Calculator
Turn the dose printed on a fish medicine label into the exact amount for your tank. Enter the label dose, your water volume and the number of treatments, and get the dose per treatment and for the whole course.
How to use this calculator
- Copy the dose from the label, for example "5 mL per 10 gallons" or "1 packet per 10 gallons". Use the first-day dose if the label gives a different starting dose.
- Enter your tank volume and how much of it is taken up by gravel, rock and decorations. 10 to 15% is typical for a tank with a normal gravel bed. If you are not sure of your volume, use the aquarium volume calculator.
- Enter the number of doses the label asks for, so you know how much product to buy for the full course.
- Measure accurately. Use a syringe for liquids and a 0.01 g scale for powders. Household spoons vary a lot.
Before you dose: safety checklist
- Remove activated carbon and other chemical filter media. Carbon absorbs many medications. US federal labelling rules for at least one aquarium drug say to disconnect carbon filtration during treatment while keeping aeration running.
- Keep aeration running. The same labelling rules ask for adequate aeration during treatment, and stressed, sick fish need well-oxygenated water. An air stone or extra surface movement is a sensible precaution.
- Check invertebrate and plant safety. Copper treatments such as Seachem Cupramine are labelled "not for use in aquariums housing invertebrates". Shrimp, snails and some plants are sensitive to many treatments. Use a hospital tank if your display has them.
- Check freshwater vs saltwater dosing. Some products use a different dose in freshwater. Cupramine, for example, uses half dose in freshwater.
- Do not mix medications unless the label says it is safe.
- After treatment, do a water change and put fresh carbon back in to remove what is left.
Formula used
Dose = label amount × (real water ÷ label volume)
Course total = dose × number of doses
Both volumes are converted to liters first, so you can mix units: a label written per US gallon works with a tank measured in liters. Conversions use 1 US gallon = 3.785 L, 1 UK gallon = 4.546 L, 1 US teaspoon = 4.929 mL and 1 US tablespoon = 14.787 mL.
Worked example
A label says 5 mL per 10 US gallons, given 3 times. Your tank is a 55 gallon with about 10% of its volume taken by gravel and rock.
Real water: 55 × 0.90 = 49.5 gallons. Dose: 5 × (49.5 ÷ 10) = 24.75 mL per treatment, or about 5.02 US teaspoons. Course total: 24.75 × 3 = 74.25 mL, so a 4 oz (118 mL) bottle is enough.
Unit converter: mg/L, ppm and mg per gallon
Some treatments and scientific papers give concentrations in mg/L (ppm) while others use mg per gallon. Use this converter to move between them.
Example: 2.7 mg/L × 3.785 = 10.22 mg per US gallon. In fresh water, 1 mg/L is the same as 1 ppm by weight because a liter of water weighs about 1 kg.
Common label units explained
| Label unit | What to watch for |
|---|---|
| mL | Most accurate for liquids. Use a syringe, not the bottle cap, for small tanks. |
| Drops | Drop size depends on the dropper. Use the dropper that came with the product. |
| Teaspoons | Labels usually mean a US level teaspoon (4.93 mL). Kitchen spoons vary. |
| Tablets, packets | For small tanks you may need part of one. Dissolve the whole tablet or packet in a known amount of tank water and dose the right share of that liquid. |
| Grams, mg | Weigh with a scale that reads to 0.01 g or better. |
Frequently asked questions
Should I dose medication for the tank size or the actual water volume?
Follow the product label first. Many labels are written per gallon or liter of water, and gravel, rock and the gap below the rim mean a tank usually holds 10 to 20 percent less water than its nominal size. Dosing for the real water volume avoids overdosing, which matters most with narrow-margin medicines such as copper.
Why do I need to remove carbon before treating fish?
Activated carbon absorbs many medications, which lowers the dose your fish actually get. Labels commonly tell you to take carbon out during treatment and keep aeration going. Carbon is then used after treatment to remove what is left.
How many drops are in a mL?
It depends on the dropper and the liquid. One manufacturer states 20 drops equals 1 mL for its own dropper bottle, but other droppers differ. Always use the dropper supplied with the product or the mL figure from the label, not a general conversion.
Is ppm the same as mg/L?
In fresh water, yes, for practical purposes. One liter of fresh water weighs about one kilogram, so 1 mg per liter is 1 part per million by weight. In seawater the difference is about 2.5 percent, which is small compared with dosing error.
Are fish medicines safe for shrimp, snails and plants?
Not always. Copper-based treatments are labelled not for use with invertebrates, and many other treatments can harm shrimp, snails or sensitive plants. Read the label, and treat fish in a separate hospital tank if your display tank has invertebrates.
Related calculators
- Aquarium volume calculator: get an accurate water volume before dosing
- Water change calculator: plan water changes after treatment
- Salinity calculator: useful for salt dips and saltwater treatments
Sources: Volume and spoon conversions from NIST, US customary to metric conversions. Carbon removal and aeration during treatment from 21 CFR 529.1526 (nifurpirinol). Invertebrate warning, freshwater half dose and carbon removal of copper from the Seachem Cupramine product information.
Last updated: October 2026