How do I convert calories back to joules?

Use the reverse converter: 1 calorie equals 4.184 J.

Is this converter accurate?

Yes. It uses the exact SI/NIST definitions of each unit and shows up to 6 significant digits.

To convert joules to calories, multiply the value by 0.239005736.

cal = J × 0.239005736

90 J × 0.239005736 = 21.51 cal

Joule (J): The SI unit of energy, one newton-metre, named after James Prescott Joule.
Calorie (cal): The thermochemical calorie is exactly 4.184 joules, historically the heat to warm one gram of water by 1 °C.

How do I convert joules to calories?: To convert joules to calories, multiply the value by 0.239005736.
How many calories are in 1 joule?: 1 joule equals 0.239006 cal.
How many calories are in 10 joules?: 10 J equals 2.39006 cal.
How do I convert calories back to joules?: Use the reverse converter: 1 calorie equals 4.184 J.
Is this converter accurate?: Yes. It uses the exact SI/NIST definitions of each unit and shows up to 6 significant digits.