Convert Water Temperature from Fahrenheit to Celsius

Direct answer

Subtract 32 from the Fahrenheit water temperature and multiply the result by 5/9.

For example, 77°F converts as follows:

Enter another reading into the Fahrenheit to Celsius Converter.

How to convert a water-temperature reading

1. Record the complete Fahrenheit reading. Include any decimal portion shown by the thermometer.
2. Subtract 32. Complete this step before multiplying.
3. Multiply by 5 and divide by 9.
4. Round the final Celsius value appropriately.
5. Keep the measurement context clear. Pool water, tap water, aquarium water, and cooking water may have different purposes and interpretation.

Common water temperatures in Fahrenheit and Celsius

Example: convert 80°F water

Example: convert 86°F water

Example: convert 104°F water

Pool-temperature conversions

Pool thermometers and heating controls may use either temperature scale. Convert the measured water temperature rather than a general weather reading.

Comfort and suitability depend on activity, age, health, air temperature, exposure time, and professional or facility guidance. Conversion alone does not determine an appropriate pool setting.

Bath and shower water temperatures

A control setting, water-heater setting, and measured tap-water temperature may not be identical. Heat can be lost through pipes, fixtures, containers, and surrounding air.

When converting a reading:

• identify where the temperature was measured;
• allow the thermometer reading to stabilize;
• keep the original unit in your record;
• avoid treating an approximate control number as an exact reading;
• follow relevant appliance and safety instructions.

Aquarium and tank readings

Aquarium thermometers, heaters, and care instructions may use Fahrenheit or Celsius. Convert the actual measured value and keep enough precision to compare it with the relevant equipment or care guidance.

Example: convert 78.8°F

A unit converter does not determine the correct temperature for a particular species or system.

Water freezing and boiling points

Two important reference points are:

Actual phase-change temperatures can be affected by pressure, elevation, dissolved substances, and measurement conditions. The familiar values are standard reference points.

Measured temperature versus control setting

A heater or appliance setting may represent a target rather than the exact current water temperature. Thermostats also cycle and may permit small temperature variations.

Before converting, identify whether the number describes:

• the current measured water temperature;
• a target setting;
• a maximum setting;
• a relative control level;
• an alert threshold.

Thermometer precision and rounding

If a thermometer displays 82.4°F, convert that complete reading before rounding.

A thermometer that displays only whole Fahrenheit degrees does not justify reporting a converted value to many decimal places.

Common water-temperature conversion mistakes

Converting the air temperature instead of the water

Air and water can have different temperatures. Convert the reading that applies to the intended measurement.

Using the mental weather shortcut

Subtracting 30 and dividing by 2 is only an estimate and may be unsuitable near an important threshold.

Treating a control number as a measured temperature

Some controls use relative levels rather than Fahrenheit degrees.

Rounding the input before conversion

Convert decimal thermometer readings directly.

Using conversion as safety or care guidance

The calculation changes the unit but does not determine whether a water temperature is suitable for a person, animal, process, or appliance.

Related Fahrenheit to Celsius guides

Frequently asked questions