CGS to SI Unit Converter

About the CGS to SI Unit Converter

The centimetre-gram-second (CGS) system of units was the dominant measurement system in physics for over a century before the International System of Units (SI) became the global standard. Many older textbooks, research papers, and specialized fields — particularly electromagnetism and astrophysics — still use CGS units like the dyne, erg, gauss, poise, and stokes. Converting between CGS and SI is essential when working with legacy literature or cross-referencing data.

This CGS-to-SI converter handles ten key physical quantities: force (dyne ↔ newton), energy (erg ↔ joule), pressure (barye ↔ pascal), dynamic viscosity (poise ↔ pascal-second), kinematic viscosity (stokes ↔ m²/s), magnetic flux density (gauss ↔ tesla), magnetic flux (maxwell ↔ weber), magnetic field strength (oersted ↔ A/m), luminance (stilb ↔ cd/m²), and acceleration (gal ↔ m/s²).

Select the physical quantity, choose the direction, enter a value, and get the conversion. The tool includes a complete reference table of all CGS-SI factors, quick preset buttons, and scientific notation outputs for very large or very small values commonly encountered in physics.

When This Page Helps

CGS units appear frequently in astrophysics, materials science, and older engineering references. Manually recalling conversion factors like 1 dyne = 10⁻⁵ N or 1 gauss = 10⁻⁴ T is time-consuming and error-prone. It gives instant, accurate bidirectional conversion for the ten most important CGS-SI quantity pairs used in practical academic and industrial workflows.

How to Use the Inputs

1. Select the physical quantity (e.g., Force, Energy, Magnetic Flux Density) from the dropdown.
2. Choose the conversion direction: CGS → SI or SI → CGS.
3. Enter the numeric value in the input field.
4. Read the converted result in both standard and scientific notation.
5. Use preset buttons to quickly test common conversions (e.g., 1 dyne → N).
6. Review the full CGS ↔ SI reference table for all ten quantities and their conversion factors.

Example Calculation

Tips & Best Practices

• In CGS-Gaussian electromagnetism, electric and magnetic fields have the same dimensions — this is not the case in SI.
• The gal (cm/s²) is still officially used in gravimetry and geodesy to express gravitational acceleration.
• Viscosity in poise is common in materials science; 1 centipoise (cP) = 1 mPa·s, which is the viscosity of water at 20°C.
• Magnetic field strength in gauss is still widely used in everyday contexts (e.g., refrigerator magnets are ~50 G).
• The erg is tiny — about the kinetic energy of a mosquito in flight. One joule equals 10 million ergs.
• When converting CGS electromagnetic units, be aware that there are three CGS subsystems (Gaussian, ESU, EMU) with different conventions.

History of the CGS System

The CGS system was introduced by the British Association for the Advancement of Science in 1874. It became the standard in physics and engineering until the mid-20th century when the MKS (metre-kilogram-second) system, later formalized as SI, gained dominance. The transition was formalized in 1960 when the General Conference on Weights and Measures adopted SI.

CGS Electromagnetic Subsystems

Three variants exist for electromagnetic quantities: CGS-ESU (electrostatic units), CGS-EMU (electromagnetic units), and CGS-Gaussian (a hybrid). Each defines charge, current, and field differently, leading to different conversion factors to SI. The Gaussian system is most common in theoretical physics.

When CGS Is Still Preferred

Astrophysics journals (e.g., ApJ, MNRAS) commonly use CGS. Gravitational acceleration is measured in gals in geodesy. Material hardness testers report in CGS-derived units. Understanding both systems and converting between them is a practical necessity for researchers working across disciplines.

Frequently Asked Questions

• What is the CGS system?

  The CGS (centimetre-gram-second) system defines base units as the centimetre for length, gram for mass, and second for time. Derived units like dyne, erg, and poise follow from these base units.

• Why do some fields still use CGS?

  Astrophysics, plasma physics, and some materials science journals use CGS because the Gaussian CGS electromagnetic equations are simpler (no ε₀ or µ₀ constants). Legacy literature also keeps CGS relevant.

• How do I convert gauss to tesla?

  Multiply by 10⁻⁴. So 1 gauss = 0.0001 tesla, or equivalently 10,000 gauss = 1 tesla.

• What is a dyne?

  A dyne is the CGS unit of force. It is the force needed to accelerate 1 gram at 1 cm/s². One newton equals 100,000 dynes.

• How do ergs relate to joules?

  One erg = 10⁻⁷ joules, so 1 joule = 10,000,000 ergs. The erg is very small — roughly the energy of a grain of sand falling 1 cm.

• What is poise used for?

  Poise measures dynamic viscosity. Water at 20°C has a viscosity of about 1 centipoise (0.01 poise). Honey is approximately 2,000–10,000 centipoise depending on type and temperature.