Liters, gallons, °F/°C, cm/inches, dGH/ppm/mmol – convert live, right here.
Gallons: US listings (e.g. a "20 gallon long") almost always mean US gallons (3.79 L). British manufacturers use the slightly larger UK gallon (4.55 L).
Fahrenheit: US heaters and thermostats often display °F instead of °C – important when importing equipment.
dGH vs. ppm/mmol: European test kits (JBL, Dennerle, Sera) measure in dGH. Imported or American kits (API) often give ppm CaCO₃ or mmol/L instead.
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1 US gallon equals 3.78541 liters. A UK (Imperial) gallon is slightly larger at 4.54609 liters – for aquarium sizes given in gallons (e.g. a "55 gallon tank"), always check which gallon is meant.
°C = (°F − 32) × 5/9. On US heaters/thermometers using a Fahrenheit scale, 78°F is about 25.6°C – a common target range for most tropical freshwater tanks.
dGH (degrees of general hardness, German scale) is common on European test kits. American/British kits often report ppm (parts per million CaCO₃) or mmol/L instead. 1 dGH ≈ 17.85 ppm ≈ 0.179 mmol/L.
US and UK aquariums are usually specified in inches, European ones in cm. 1 inch = 2.54 cm – worth checking the actual fit in cm for imported equipment (filters, heaters, lights).