Instantly Convert Ergs ↔ Joules — Both Directions
Convert ergs to joules (erg → J) or joules to ergs (J → erg) instantly. Get the exact conversion with formula breakdown, reference table, and related energy unit conversions — all free, no sign-up needed.
The erg and the joule are both units of energy — one from the CGS (centimetre-gram-second) system, one from the SI (International System of Units). Our converter handles both directions instantly and accurately using the exact internationally defined conversion factor.
The erg is the unit of energy in the CGS system of units, with the symbol erg. Its name comes from the Greek word ergon (ἔργον), meaning "work." One erg is defined as the work done by a force of one dyne acting over a distance of one centimetre. It is an extremely small unit — equal to exactly 10⁻⁷ joules. The erg is widely used in astrophysics, particle physics, and spectroscopy.
The joule (symbol J) is the SI derived unit of energy, work, and heat. It is named after the English physicist James Prescott Joule (1818–1889), who made foundational contributions to thermodynamics. One joule equals the work done when a force of one newton moves an object one metre. It is also equivalent to one watt-second, one newton-metre, or one coulomb-volt — and equals exactly 10,000,000 ergs (10⁷ erg).
The exact conversion factor is 1 erg = 1 × 10⁻⁷ joules — an absolute, defined relationship with no rounding. This means one joule is ten million times larger than one erg. For the reverse direction: 1 joule = 10,000,000 ergs (1 × 10⁷ erg). All conversions on this page use this exact factor.
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The conversion between ergs and joules uses an exact, defined factor. One erg is defined as exactly 10⁻⁷ joules — this is not an approximation but an absolute relationship established by the definitions of both unit systems. Both formulas below are mathematically exact.
The table below lists common erg values converted to joules. All values use the exact factor of 1 erg = 1×10⁻⁷ J. For joules to ergs, multiply the joule value by 10,000,000 or use the converter above.
| Ergs (erg) | Joules (J) | Millijoules (mJ) | Microjoules (µJ) | Context / Notes |
|---|---|---|---|---|
| 1 erg | 1×10⁻⁷ J | 0.0001 mJ | 0.1 µJ | Work by 1 dyn over 1 cm |
| 10 erg | 1×10⁻⁶ J | 0.001 mJ | 1 µJ | Tiny energy in lab work |
| 100 erg | 1×10⁻⁵ J | 0.01 mJ | 10 µJ | — |
| 1,000 erg | 0.0001 J | 0.1 mJ | 100 µJ | — |
| 10,000 erg | 0.001 J | 1 mJ | 1,000 µJ | — |
| 100,000 erg | 0.01 J | 10 mJ | 10,000 µJ | — |
| 1,000,000 erg | 0.1 J | 100 mJ | 100,000 µJ | Energy of a small LED flash |
| 10,000,000 erg | 1 J | 1,000 mJ | 1,000,000 µJ | Lift 102g by 1m on Earth |
| 100,000,000 erg | 10 J | 10,000 mJ | — | Energy of a 1W bulb for 10s |
| 1,000,000,000 erg | 100 J | 100,000 mJ | — | ~1/3 of a food calorie (kcal) |
| 4,184,000,000 erg | 418.4 J | — | — | ≈ 1 food calorie (kcal) |
| 3.6×10¹³ erg | 3,600,000 J | — | — | 1 kilowatt-hour (kWh) |
Need to convert the other way? The table below shows common joule values converted to ergs. All values use the exact factor of 1 J = 10,000,000 erg (1×10⁷).
| Joules (J) | Ergs (erg) | Scientific Notation | Context / Notes |
|---|---|---|---|
| 0.000001 J (1 µJ) | 10 erg | 1×10¹ erg | Microjoule |
| 0.001 J (1 mJ) | 10,000 erg | 1×10⁴ erg | Millijoule |
| 0.01 J | 100,000 erg | 1×10⁵ erg | — |
| 0.1 J | 1,000,000 erg | 1×10⁶ erg | — |
| 1 J | 10,000,000 erg | 1×10⁷ erg | SI base energy unit |
| 10 J | 100,000,000 erg | 1×10⁸ erg | — |
| 100 J | 1,000,000,000 erg | 1×10⁹ erg | ~1/4 food calorie |
| 1,000 J (1 kJ) | 10,000,000,000 erg | 1×10¹⁰ erg | 1 kilojoule |
| 4,184 J | 4.184×10¹⁰ erg | ~4.18×10¹⁰ erg | 1 food calorie (kcal) |
| 3,600,000 J (1 kWh) | 3.6×10¹³ erg | 3.6×10¹³ erg | 1 kilowatt-hour |
The erg-to-joule conversion is commonly needed in scientific and academic fields where CGS and SI unit systems are both used. Here are the most common scenarios where this conversion is essential.
Astrophysicists traditionally use ergs to express stellar luminosities, gamma-ray burst energies, and X-ray emissions. For example, the Sun's luminosity is about 3.83×10³³ erg/s. When publishing in SI-compliant journals or collaborating internationally, converting to joules or watts is required.
In older physics literature — particularly pre-1970s texts — energy values are often given in ergs. Students and researchers reading classic papers by Fermi, Dirac, or Feynman will encounter ergs and need to convert them to joules or electronvolts (eV) for modern comparisons. 1 erg = 6.242×10¹¹ eV.
Physics students frequently encounter the erg in CGS-based textbooks, particularly in courses covering thermodynamics, mechanics, and electromagnetism. Converting between erg and joule is a standard dimensional analysis exercise. The exact factor (10⁻⁷) makes it a clean, simple conversion to learn.
Earthquake energy was historically expressed in ergs. The Richter scale magnitudes correspond to erg-based energy estimates — for example, a magnitude 6.0 earthquake releases approximately 6.3×10²⁰ ergs, equal to about 6.3×10¹³ joules or ~63 terajoules. Modern seismology now uses joules and the moment magnitude scale.
In molecular spectroscopy and quantum chemistry, the erg per molecule is sometimes used alongside electronvolts and joules. Bond dissociation energies, photon energies, and vibrational energy levels may be expressed in ergs in older literature, requiring conversion to SI joules for modern computational chemistry work.
Engineers and scientists switching between CGS and SI systems encounter ergs frequently. The CGS system uses ergs for energy, dynes for force, and centimetres/grams/seconds as base units. Converting CGS results to SI (joules, newtons, metres, kilograms) is a routine step in international scientific communication and publication.
The National Institute of Standards and Technology (NIST) publishes the official SI unit definitions, including the joule. Their guide covers all SI base and derived units with exact definitions and conversion factors.
NIST SI Units Guide →NASA's High Energy Astrophysics Science Archive (HEASARC) uses ergs extensively in its data products. Their unit conversion pages are useful for astrophysicists working with CGS quantities like erg/s and erg/cm².
NASA HEASARC Tools →The CGS system that defines the erg has a rich history going back to Maxwell and Kelvin in the 1860s. Understanding its origins helps clarify why both CGS and SI units coexist in modern physics literature.
CGS System — Wikipedia →