Converting between Celsius and Fahrenheit

Students use the two conversion formulas and check their units.

• Fahrenheit to Celsius: C = (F − 32) × 5/9
• Celsius to Fahrenheit: F = C × 9/5 + 32
• Rounding to the nearest tenth when the result is not exact

Evaluating a formula at a given value is standard 6.EE.A.2.c, and the multiply-then-add structure uses the ratio thinking of 6.RP.A.3.d. Body temperature (98.6 °F, 37 °C) and boiling water (212 °F, 100 °C) are good anchors to keep in mind.

Write both formulas at the top of the page before starting, and allow a calculator if the goal is the formula rather than the arithmetic.

• Identify the starting unit, then pick the matching formula.
• Do the operations in order: subtract 32 first when starting from Fahrenheit.
• Round only at the end, then choose the answer whose number and unit both match.

Use page two to check, and ask for the working on any item that was wrong.

• Order of operations: multiplying 44 by 5/9 before subtracting 32 gives a very wrong answer.
• Wrong formula: using 9/5 when going from Fahrenheit to Celsius.
• Unit traps: 37 °F and 37 °C are very different, and several choices only change the symbol.
• Rounding too early, which can turn 6.7 °C into 6.6 °C.

Next, review comparing temperatures above and below zero, or go back to metric conversions for more ratio practice.