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Erg to Joule Converter

Enter an energy in ergs to convert to joules and calories.

How it is calculated

The conversion is J = erg × 10−7, because 1 erg is 10−7 joule. The calorie figure is then cal = J × 0.239005736, the factor for the small (gram) calorie of 4.184 J. This is not the food Calorie (kcal), which is 1000 times larger. Both results are printed with nine decimals so that small energies do not collapse to zero: a single erg shows as 0.000000100 J. Negative and decimal inputs are accepted and converted as entered. Joule or calorie values of 1015 or more, such as astrophysical energies, are printed in scientific notation (1e51 erg gives 1.0000 × 1044 J); smaller values keep the nine decimals.

Worked example

A lab note gives an energy of 5,000,000 erg (5 × 106). Joules: 5,000,000 × 10−7 = 0.5, which the tool prints as 0.500000000 J. Calories: 0.5 × 0.239005736 = 0.119502868 cal. So 5 million ergs is half a joule, a little over a tenth of a small calorie.

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Common mistakes

  • Treating the calorie result as food Calories. It is the small calorie; divide by 1000 for kilocalories.
  • Typing powers of ten as 10^7. That gives no result; type plain digits (10000000) or 1e7.
  • Mixing erg with other CGS units such as dyne (force) or erg per second (power). An erg is energy only.
  • Assuming the joule value will be exact for tiny inputs: the output stops at nine decimals, so a very small energy loses its trailing digits.
  • Confusing erg with electronvolt. 1 eV is about 1.6 × 10−12 erg, and this tool does not convert it.

Sources

About this calculator

The erg is the unit of energy in the CGS (centimetre-gram-second) system, defined as the work done by a force of one dyne acting over a distance of one centimetre. Because the SI system uses metres, kilograms and seconds instead, 1 erg equals exactly 10⁻⁷ joules — an erg is a tiny amount of energy, about what a mosquito uses to take off.

This calculator converts an energy value from ergs to joules and to calories, which is useful whenever older physics texts, spectroscopy data, or astrophysical papers quote energies in CGS units and a modern SI or everyday figure is needed for comparison or further calculation.

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Comments (1)

  • Editorial team

    Since an erg is exactly 10⁻⁷ joule, you can check any result by moving the decimal point seven places left. This page prints nine decimals, so it is poorly suited to single-photon energies: a visible photon of about 3.3 × 10⁻¹² erg shows as 0.000000000 J here. For such tiny values, shift the decimal yourself and keep the exponent. Which kind of source quotes your energies in ergs, an old textbook or an astrophysics paper?

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