Aquarium Unit Converter
Convert between metric and imperial units used in fishkeeping. Temperature, volume, and length - all in one place.
Fishkeeping crosses borders, and so do the units on your equipment. Your heater might show Fahrenheit while your thermometer reads Celsius. Product labels might list US gallons while you think in litres. This converter handles the three unit categories you encounter most often in the hobby - temperature, volume, and length - so you can get the right number without reaching for a search engine.
Select a category, choose your units, and type in either field. The conversion happens in real time - no button to press.
Quick reference
- 25 C = 77 F (typical tropical)
- 1 litre = 0.264 US gal
- 1 US gallon = 3.785 litres
- 1 inch = 2.54 cm
- 1 foot = 30.48 cm
Converter
Pick a category, select your units, and type in either field. The other updates automatically.
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Conversion Formulas
The formulas behind each conversion. All are standard mathematical ratios except temperature, which uses an offset.
Temperature
F = C x 9/5 + 32
C = (F - 32) x 5/9
Multiply Celsius by 9/5 and add 32 to get Fahrenheit. Subtract 32 from Fahrenheit and multiply by 5/9 to get Celsius.
Volume
1 litre = 0.264172 US gal
1 litre = 0.219969 UK gal
1 US gal = 3.78541 litres
1 UK gal = 4.54609 litres
All volume conversions go through litres as the base unit. UK gallons are about 20% larger than US gallons.
Length
1 inch = 2.54 cm
1 foot = 30.48 cm
1 metre = 100 cm
All length conversions go through centimetres as the base unit. One foot equals exactly 12 inches.
Common Aquarium Values
Tropical fish temperature range
24-28 C = 75-82 F
Covers most common tropical species including tetras, barbs, gouramis, and livebearers.
Coldwater fish temperature range
15-22 C = 59-72 F
Suitable for goldfish, white cloud mountain minnows, and hillstream loaches.
Common tank sizes
10 US gal = 37.9 litres = 8.3 UK gal
20 US gal = 75.7 litres = 16.7 UK gal
55 US gal = 208.2 litres = 45.8 UK gal
75 US gal = 283.9 litres = 62.5 UK gal
Standard tank lengths
60 cm = 23.6 in = 2.0 ft
90 cm = 35.4 in = 3.0 ft
120 cm = 47.2 in = 3.9 ft
150 cm = 59.1 in = 4.9 ft
Why unit mismatches matter
Confusing US gallons with UK gallons when dosing medication can mean a 20% overdose or underdose. Setting a heater to 78 when it reads in Celsius instead of Fahrenheit would heat your tank to 172 F - a fatal mistake. Always confirm which units your equipment and products use before making adjustments.
Tip for dosing products
When a product says "1 ml per gallon," check if it means US or UK gallons. Most American brands mean US gallons. Most British brands mean imperial (UK) gallons. When in doubt, dose for the smaller unit (US gallons) and increase gradually - it is safer to slightly underdose than overdose.
Frequently Asked Questions
Common questions about unit conversions in fishkeeping.
Why do aquarium products use different unit systems?
Aquarium products are manufactured and sold worldwide. North American products typically use Fahrenheit, US gallons, and inches, while European and Asian products use Celsius, litres, and centimetres. UK products sometimes use imperial gallons, which are larger than US gallons. Always check which unit system a product label is using before dosing or sizing equipment.
What is the difference between US gallons and UK gallons?
A US gallon is 3.785 litres, while a UK (imperial) gallon is 4.546 litres - about 20% larger. Most aquarium products sold in the United States use US gallons. If you are in the UK, double-check whether equipment ratings refer to imperial or US gallons, as the difference matters for dosing and filtration sizing.
What temperature range do most tropical fish need?
Most tropical freshwater fish thrive between 24-28 degrees Celsius (75-82 degrees Fahrenheit). Some species like discus prefer the warmer end (28-30 C / 82-86 F), while others like white cloud mountain minnows do well at cooler temperatures (18-22 C / 64-72 F). Always research the specific needs of your species.
Why does my heater show Fahrenheit but my thermometer shows Celsius?
Heaters and thermometers are often manufactured in different countries, so they may use different unit systems. This is one of the most common reasons fishkeepers need a temperature converter. Set your heater to the equivalent of your target Celsius temperature using this converter.
How do I convert tank dimensions to find volume?
This converter handles individual unit conversions (e.g. centimetres to inches). To calculate your full tank volume from dimensions, use our dedicated Aquarium Volume Calculator which accepts measurements in either centimetres or inches and gives you volume in litres, US gallons, and UK gallons.
Are these conversions exact?
Yes. The conversions use standard mathematical ratios (e.g. 1 inch = 2.54 cm exactly, 1 US gallon = 3.78541 litres). Results are rounded to four decimal places for readability, which is far more precision than you need for any aquarium application.
Related Guides
Learn more about the units and measurements that matter for your aquarium.
Water Temperature Guide
Why stable temperature matters, how to monitor it, and what happens when it fluctuates too much.
Read the guideWater Changes
How often to change water, how much to replace, and the right way to do it without stressing your fish.
Read the guideTank Setup Guide
A step-by-step walkthrough of setting up your first aquarium, including equipment placement and cycling.
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