Pet care crosses borders more than almost any other household topic. A fish keeper in the United States reads a care sheet written in Celsius. A dog owner in Britain uses a thermometer in Fahrenheit that a vet in America quoted. A raw feeder follows food-safety advice given for a fridge in either scale. The conversion is simple, but it is easy to get wrong in your head, especially for differences and for negative numbers. This guide gives the two formulas, a table of the temperatures pet owners most often meet, the rule for converting a change rather than a reading and a note on why this guide does not say what is normal for any animal. The Pet Temperature Converter does the sum.
The formulas
°F = °C × 9 ÷ 5 + 32 °C = (°F − 32) × 5 ÷ 9
| Celsius | Working | Fahrenheit |
|---|---|---|
| 0 | 0 × 1.8 + 32 | 32 |
| 20 | 20 × 1.8 + 32 | 68 |
| 25 | 25 × 1.8 + 32 | 77 |
| 100 | 100 × 1.8 + 32 | 212 |
The multiplier 9/5 is 1.8. A quick mental version is to double the Celsius number, take off 10% of the result and add 32. For 25 °C: double is 50, minus 5 is 45, plus 32 is 77. That works well for ordinary temperatures, and it is exact for this example.
A table for the temperatures pet owners meet
| °C | °F | Where you might see it |
|---|---|---|
| −18 | −0.4 (about 0) | Freezer setting for stored food |
| 4 | 39.2 | Fridge setting |
| 15 | 59.0 | A cool room or hall |
| 18 | 64.4 | A cool living room |
| 20 | 68.0 | A typical room |
| 22 | 71.6 | A warm room |
| 24 | 75.2 | A warm room, or a cool tank |
| 25 | 77.0 | A tropical tank target in many care sheets |
| 26 | 78.8 | A warmer tank |
| 28 | 82.4 | A very warm room, or a warm tank |
| 30 | 86.0 | A hot day |
| 35 | 95.0 | A very hot day |
(These are the values, not recommendations. Which of them is right for an animal depends on the species and on your vet’s advice.)
Converting a difference
A temperature reading and a temperature change are converted differently. A reading has the offset of 32 between the scales. A difference does not, because both ends of the difference shift by the same 32.
| Change | Working | Equivalent |
|---|---|---|
| 1 °C | × 1.8 | 1.8 °F |
| 3 °C | 3 × 1.8 | 5.4 °F |
| 5 °C | 5 × 1.8 | 9.0 °F |
| 10 °F | 10 ÷ 1.8 | 5.6 °C |
If a tank heater is set to a range of ±1 °C around 25 °C, that is 24 to 26 °C, or 75.2 to 78.8 °F, a spread of 3.6 °F. If someone tells you the room dropped by 5 °C overnight, the Fahrenheit drop is 9 °F, not 41 °F. The error of adding 32 to a difference is common, and it can make a harmless swing look dangerous.
Aquariums and ponds
Fish are sensitive to temperature, and care sheets give a range for each species. Convert the range at both ends, and write both scales next to your thermometer.
| Care sheet range (°C) | In °F |
|---|---|
| 22 to 26 | 71.6 to 78.8 |
| 24 to 27 | 75.2 to 80.6 |
| 18 to 22 | 64.4 to 71.6 |
Do not rely on a single reading in one place. Check the thermometer against a second one, and read it at the same time each day. For a pond, the temperature changes with the seasons and the depth, and your supplier or a species guide gives the limits for your fish. Our guide to water changes explains why the new water should be close to the tank’s temperature. The right target is a matter for the care sheet, not for this guide.
Food storage
For stored pet food, the figures to know are the fridge and freezer settings. Food-safety guidance in the United States gives a fridge setting at or below 40 °F (4 °C) and a freezer at 0 °F (−18 °C). Other countries give similar numbers in Celsius. If you feed raw or fresh food, check your own fridge with a separate thermometer and follow the guidance for your country. The conversions are 4 °C = 39.2 °F and −18 °C = −0.4 °F, which is 0 °F to the nearest degree.
A note on body temperature
This guide does not list the normal body temperature of any animal, and it does not interpret a reading. Normal values differ by species and by the way of measuring, and a temperature that matters is one for your vet to read in context. What the converter does is stop a unit error: if a vet says a number in one scale and your thermometer shows another, convert before you compare. If you are worried about a pet’s temperature, phone your vet and tell them both the number and the scale of the thermometer.
Heat and weather
Warm weather is a welfare matter for pets. When you read a forecast in one scale and a guide in another, convert and compare. Our guide to dog hydration in hot weather gives the water arithmetic. The conversion tells you what 30 °C is in your own units (86 °F), but how a particular dog copes depends on its breed, age, coat and health.
Other conversions
Pet care involves more than one set of units. Weights and lengths have their own factors, which our other guides cover. See kilograms to pounds for pets and the dog measurement chart in centimetres and inches. The Pet Measurement Converter and Pet Weight Converter handle those.
A worked example
Elena has moved from the United States to Ireland. Her new aquarium care sheet says 24 to 26 °C. Her thermometer, bought in the US, shows °F. The room has dropped 4 °C this week, according to the weather report.
| Question | Working | Answer |
|---|---|---|
| Tank range in °F | 24 × 1.8 + 32; 26 × 1.8 + 32 | 75.2 to 78.8 °F |
| Is 77 °F in range? | 77 is between 75.2 and 78.8 | Yes |
| Room drop in °F | 4 × 1.8 | 7.2 °F |
| Fridge at 4 °C in °F | 4 × 1.8 + 32 | 39.2 °F |
Elena writes the 75.2 to 78.8 °F range on a card next to the tank. She notes that a 7.2 °F drop in the room is not the same as a 7.2 °F drop in the tank, and she asks her supplier whether anything needs adjusting. The calculations took a minute and avoided a week of guessing.
Checking the mental shortcut
The shortcut “double it, take off a tenth, add 32” is handy, and worth testing against the exact answer.
| °C | Shortcut | Exact |
|---|---|---|
| 10 | 20 − 2 + 32 = 50 | 50.0 |
| 20 | 40 − 4 + 32 = 68 | 68.0 |
| 25 | 50 − 5 + 32 = 77 | 77.0 |
| 30 | 60 − 6 + 32 = 86 | 86.0 |
| 37 | 74 − 7.4 + 32 = 98.6 | 98.6 |
The shortcut is exact because doubling and taking off a tenth is multiplying by 1.8. It works well for any value, so you can use it on a thermometer reading without a calculator. One more fact is worth remembering: the two scales meet at −40, where −40 °C is −40 °F.
Reading digital thermometers
Many digital thermometers show one decimal place. Do not round before you convert. A reading of 25.3 °C is 77.5 °F (25.3 × 1.8 + 32 = 77.54), while rounding to 25 first gives 77.0, half a degree out. For a tank with a narrow range, half a degree is worth keeping. Calibrate a new thermometer against a second one, and remember that where you put the probe matters as much as the scale.
Common mistakes
- Adding 32 when converting a difference.
- Reading a thermometer in the wrong scale.
- Rounding too early on a narrow care-sheet range.
- Using one thermometer without a check.
- Taking a food-safety figure from a different country without checking.
- Treating a conversion as advice on what is normal.
- Mixing up the formulas for the two directions.
Quick summary
- °F = °C × 9/5 + 32; °C = (°F − 32) × 5/9.
- 25 °C is 77 °F, 20 °C is 68 °F, 4 °C is 39.2 °F, and −18 °C is about 0 °F.
- A difference converts with 1.8 alone: 5 °C is 9 °F.
- Write both scales next to a tank thermometer and fridge.
- Ask your vet or the care sheet what is right; the converter only changes units.
- Use the Pet Temperature Converter.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9, divide by 5 and add 32. For 25 °C: 25 × 9 ÷ 5 + 32 = 77 °F.
How do I convert Fahrenheit to Celsius?
Subtract 32, multiply by 5 and divide by 9. For 68 °F: 36 × 5 ÷ 9 = 20 °C.
How do I convert a temperature difference?
Multiply a Celsius difference by 1.8 without adding 32. A 3 °C change is 5.4 °F.
What temperature is normal for my pet?
Ask your vet. Normal ranges depend on the species and the situation, and a calculator cannot tell you what a reading means.
What temperature should an aquarium be?
It depends on the species. Use the care sheet for your fish and convert the figure; this guide only does the conversion.
What is the freezer setting for storing raw pet food?
Food-safety guidance commonly gives −18 °C, or 0 °F, for freezer storage. Check the guidance in your country.
Sources
- Standard temperature conversion: °F = °C × 9/5 + 32 (NIST Guide to the SI, SP 811)
- USDA FSIS: freezer storage at 0 °F (−18 °C) keeps food safe indefinitely; refrigerators should be at 40 °F (4 °C) or below
Related calculators
- Pet Temperature ConverterConvert aquarium, room and water temperatures between Celsius and Fahrenheit.
- Pet Measurement ConverterConvert crate, collar, harness and coat measurements between centimetres and inches.
- Pet Weight ConverterConvert your pet's weight between kilograms, pounds, ounces and grams.
Keep reading
- Dog Hydration in Hot Weather: A Practical PlanA practical hot-weather hydration plan for dogs: the 50 mL per kg reference, water on walks and in the car, measuring intake and when to call a vet at once.
- Kilograms to Pounds for Pets: A Quick ChartA kilograms to pounds chart for pets from 1 to 50 kg, plus grams to ounces for kittens and small animals, the exact conversion factors and common weight mix-ups.
- Dog Measurement Chart: Centimetres to InchesA centimetres to inches chart for dog measurements: chest, neck, length and height for harnesses, crates, beds and coats, with the exact factor and measuring tips.
- Feeding Your Dog in Pounds and OuncesConvert a dog's daily food from grams to ounces and pounds: 1 oz = 28.35 g, so 294 g is 10.37 oz. Tables, bag lengths for 22 and 33 lb bags and a rounding rule.