# How to Calculate the Mean Annual Temperature ••• Guasor/iStock/GettyImages

If you have the sneaking suspicion that the local climate has been changing over the past few years, calculating the mean annual temperature will help dispel the mystery. The mean annual temperature refers to the average of the maximum and minimum temperatures of a year, taking the mean average of the coldest month of the year and averaging it with the mean average of the hottest month of the year. The mean annual temperature is a valuable climatology tool that can assess an area's climate change.

#### TL;DR (Too Long; Didn't Read)

To calculate the mean or average value of a set of numbers, add all of the numbers and then divide by how many numbers in the set. For example, consider the set of numbers 3, 6, 7, 4. The sum of this sequence equals 20. To find the average, divide by 4 because the set contains 4 numbers. The average then equals 20÷4=5.

Calculate the mean daily temperatures of an area, usually a town or city, for each day of the year. Take the temperature readings on the hour for a 24-hour period. Add the hourly readings together, then divide that number by 24 to get the mean daily temperature. Record the first measurement at midnight and the last at 11 p.m. of the same day.

Calculate the mean monthly temperature by adding up the daily mean temperatures for each day of a month and then dividing that sum by the number of days in the month. For example, for the month of January, add up the 31 mean daily temperatures, then divide by 31. For the month of February, add the 28 mean daily temperatures together, then divide by 28 (in leap years, add the 29 mean daily temperatures and divide by 29).

Calculate the average of the 12 mean monthly temperatures. Add the mean monthly temperatures for the months of the calendar year, January to December, together, and then divide by 12. This will be the mean annual temperature.

#### Tips

• Two areas with very different climates can have the same mean annual temperature. A climate that has temperate weather throughout the year can have the same mean annual temperature as an area with a highly variable winter and summer.

For more precision, add the daily mean temperatures together and then divide them by the number of days of the year.

For less precision but greater ease, take the average of the highest and lowest temperature of the day to get the mean daily average.

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