Calorie (15 °C) to Joule Converter

About this calculator

The “15 °C calorie” (cal₁₅) is one of several historical, slightly different definitions of the calorie: the energy needed to raise the temperature of 1 gram of water from 14.5 °C to 15.5 °C at standard atmospheric pressure, as measured directly by calorimetry rather than defined by convention. It’s distinct from the thermochemical calorie (exactly 4.184 J) and the International Table calorie (4.1868 J) used in nutrition labeling — the differences are small, around 0.03%, but matter in precise calorimetry and older scientific literature.

This calculator converts between cal₁₅ and joules using the accepted equivalence 1 cal₁₅ = 4.1855 J, in either direction, which is the figure needed when digitizing or cross-checking older thermochemical data, physics textbooks, or calorimeter calibration records that specify energy in the 15 °C calorie rather than the modern SI joule.