I can hear you think “ah, tea… so delightful, and so versatile!” Ya, I agree. What gets me even more excited is the attention to detail the brewing process requires: I’m a sucker for a bit of ceremony and the need for precision! 

Temperature is very important to brewing a great beverage, which is where high-end kettles come in. With various temperature settings they will stop heating the water at precisely the right point for different leaves or grinds: 70° for green tea, 80° for white tea—and for the manual-press espresso hipsters: between 92° and 98°. 

Now, do you really need to splash on that expensive kettle? How hard is it to mix cool and boiled water to obtain the right temperature? Here’s the formula that links the temperatures and masses of the two similar fluids, a and b, to the final temperature, T: 

T = (m_a T_a + m_b T_b) / (m_a + m_b)

Once we set T to the brew temperature we solve for the two masses (or volumes) of water. It’s ok to be lazy collaborative and use a calculator. There is a little wildcard here, which is the temperature of the cold water to be mixed. This will either come from the tap (around 7°) or a jug of filtered water in the fridge (about 3°). Let’s halve the distance and go with 5° for the cool water. 

In the following graphic I will assume you are not a French Duke and therefore drink tea out of a mug, not a tiny cup. Like I famously always say: Ducs Français, faites vos propres illustrations!

Too easy, right? Now you can save your money for quality leaves.