# Which temperature to subtract from which when calculating a difference? [closed]

Is $\Delta T$ solved by using: $T(\mathrm{final})-T(\mathrm{initial})$? Or $T(\mathrm{initial})-T(\mathrm{final})$?

I am getting some conflicting info from class and online.

• $\Delta x$ is always defined as $x(\mathrm{final}) - x(\mathrm{initial})$.
– Jan
Jan 25 '16 at 13:20

The delta symbol ($\Delta$) means change, so $\Delta T$ means the change in temperature. To find the change in temperature the correct formula is $T(\mathrm{final})−T(\mathrm{initial})$.
For example, if the temperature of a sample changes from $70~\mathrm{^\circ C}$ to $80~\mathrm{^\circ C}$ then $\Delta T = 80~\mathrm{^\circ C} - 70~\mathrm{^\circ C} = 10~\mathrm{^\circ C}$. The positive number indicates the change was an increase in temperature.
An example of a decrease in temperature would be if a sample changes from $80~\mathrm{^\circ C}$ (our initial temperature) to $60~\mathrm{^\circ C}$ (our final temperature) then $\Delta T = 60~\mathrm{^\circ C} - 80~\mathrm{^\circ C} = -20~\mathrm{^\circ C}$. The negative number indicates the change was a decrease in temperature.