Electrical resistance is the opposition to the flow of electric current in a conductor. It is measured in Ohms (Ω), named after German physicist Georg Simon Ohm. Resistance depends on the material's resistivity, length, cross-sectional area, and temperature. The SI unit is defined as the resistance between two points of a conductor when a constant potential difference of 1 volt produces a current of 1 ampere.
Resistance Converter
Convert between Ohm (Ω), Kiloohm (kΩ), Megaohm (MΩ), Gigaohm (GΩ), and 13+ other electrical resistance units with scientific precision based on SI standards.
Conversion Formula
1 Ohm = 1 Ohm
Common Resistance Conversions
Quick reference from 1 Ohm| From (1 Ω) | To Unit | Result |
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What is Electrical Resistance?
Electrical resistance is a fundamental property of materials that quantifies how strongly they oppose the flow of electric current. It is the electrical analog of mechanical friction. The SI unit of resistance is the Ohm (Ω), named after German physicist Georg Simon Ohm (1789–1854), who first formulated the relationship between voltage, current, and resistance in 1827.
Resistance depends on four factors: the material's resistivity (ρ), the length (L) of the conductor, its cross-sectional area (A), and its temperature. The relationship is expressed as: R = L/A. Conductors like copper and silver have low resistance, while insulators like rubber and glass have extremely high resistance.
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SI Unit: Ohm (Ω) One ohm is defined as the resistance when 1 volt produces 1 ampere of current.
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Symbol: Ω (Omega) The Greek letter Omega represents the ohm in circuit diagrams and equations.
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Dimension: [M L² T⁻³ I⁻²] Resistance has dimensions of mass × length² / (time³ × current²).
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Temperature Dependent Most metals increase resistance with temperature; semiconductors decrease.
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Measured with Ohmmeter Specialized multimeters measure resistance by applying a known voltage and measuring current.
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Reciprocal: Conductance The reciprocal of resistance is conductance, measured in Siemens (S) or mhos (℧).
Essential Resistance Formulas
These fundamental formulas govern electrical resistance calculations in circuits. Understanding them is essential for electrical engineers, physicists, and electronics hobbyists.
Ohm's Law
V = I × R
Voltage equals current times resistance. The foundational law of circuit analysis.
Series Resistors
R = R₁ + R₂ + R₃
Resistances add directly when connected in series. Total resistance increases.
Parallel Resistors
1/Rₜ = 1/R₁ + 1/R₂
Reciprocals add in parallel. Total resistance is always less than the smallest resistor.
Resistivity Formula
R = ρL / A
Resistance depends on resistivity (ρ), length (L), and cross-sectional area (A).
Power Dissipation
P = I² × R
Power dissipated as heat in a resistor. Also P = V²/R or P = V × I.
Temperature Coefficient
Rₜ = R₀(1 + αΔT)
Resistance changes with temperature. α is the temperature coefficient of resistivity.
Resistance Units Reference
A complete reference of all 17 resistance units supported by this converter, from the smallest picoohm to the largest statohm.
| Unit | Symbol | Equals (in Ohms) | Typical Use |
|---|---|---|---|
| Picoohm | pΩ | 10⁻¹² Ω | Superconductor research |
| Nanoohm | nΩ | 10⁻ Ω | Precision measurements |
| Microohm | μΩ | 10⁻ Ω | Contact resistance testing |
| Milliohm | mΩ | 10⁻³ Ω | PCB traces, connectors |
| Ohm | Ω | 1 Ω | Standard resistors |
| Kiloohm | kΩ | 10³ Ω | Electronic circuits |
| Megaohm | MΩ | 10⁶ Ω | Insulation testing |
| Gigaohm | GΩ | 10 Ω | High-voltage insulation |
| Teraohm | TΩ | 10¹² Ω | Dielectric measurements |
| Statohm | statΩ | 8.988×10¹¹ Ω | CGS electrostatic system |
| AbOhm | abΩ | 10⁻ Ω | CGS electromagnetic system |
| EMU of Resistance | EMU | 10⁹ Ω | Electromagnetic units |
| ESU of Resistance | ESU | 8.988×10¹¹ Ω | Electrostatic units |
| Volt per Ampere | V/A | 1 Ω | Derived SI unit |
| Reciprocal Siemens | 1/S | 1 Ω | Conductance reciprocal |
| Quantized Hall R. | Rₖ | 25,812.807 Ω | Quantum Hall standard |
| Wave Impedance | Z₀ | 376.730 Ω | Free space impedance |
Applications of Resistance Measurement
Resistance measurement is critical across industries. From consumer electronics to power transmission, accurate resistance conversion enables engineers to design safe, efficient systems.
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Electronics Design Selecting resistor values for circuits, filters, amplifiers, and voltage dividers.
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Power Systems Calculating transmission line losses, transformer winding resistance, and grounding systems.
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Insulation Testing Measuring megaohm and gigaohm resistance to verify cable and equipment insulation integrity.
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Medical Devices ECG electrodes, defibrillators, and bioimpedance measurements require precise resistance values.
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Semiconductor Industry Characterizing wafer resistivity, contact resistance, and thin-film properties at microohm levels.
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Quantum Physics Quantized Hall Resistance serves as the international standard for resistance calibration since 1990.
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Telecommunications Impedance matching in RF circuits uses the wave impedance of free space (376.73 Ω).
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Automotive Industry Battery internal resistance, sensor calibration, and ECU circuit design all depend on accurate resistance values.
Frequently Asked Questions
To convert Ohms to Kiloohms, divide the value by 1,000. For example, 5,000 Ohms equals 5 Kiloohms (5,000 ÷ 1,000 = 5 kΩ). Conversely, to convert Kiloohms to Ohms, multiply by 1,000. Similarly, 1 Megaohm = 1,000 Kiloohms = 1,000,000 Ohms, and 1 Gigaohm = 1,000 Megaohms.
These are metric prefixes of the Ohm representing different orders of magnitude:
- 1 Kiloohm (kΩ) = 1,000 Ohms — typical resistor values
- 1 Megaohm (MΩ) = 1,000,000 Ohms — insulation testing
- 1 Gigaohm (GΩ) = 1,000,000,000 Ohms — high-voltage insulation
- 1 Teraohm (TΩ) = 1,000,000,000,000 Ohms — dielectric measurements
Ohm's Law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. The formula is V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. This fundamental law, discovered by Georg Ohm in 1827, is the basis of all electrical circuit analysis.
Quantized Hall Resistance (R) is a fundamental physical constant equal to approximately 25,812.80745 Ohms. It arises from the quantum Hall effect and is defined as h/e², where h is Planck's constant and e is the elementary charge. Since 1990, it has been used as the international standard for resistance calibration by the BIPM (Bureau International des Poids et Mesures).
Series: R_total = R₁ + R₂ + R₃ + ... (resistances add directly, total increases).
Parallel: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ... (reciprocals add, total is less than smallest).
For two resistors in parallel, a simpler formula is: R_total = (R₁ × R₂) / (R₁ + R₂).
Parallel: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ... (reciprocals add, total is less than smallest).
For two resistors in parallel, a simpler formula is: R_total = (R₁ × R₂) / (R₁ + R₂).
The wave impedance of free space (Z₀) is approximately 376.730313461 Ohms. It is defined as √(μ₀/ε₀), where μ₀ is the permeability of free space and ε₀ is the permittivity of free space. This value is critical in antenna design, RF engineering, and electromagnetic wave propagation calculations.
Statohm belongs to the CGS electrostatic system (ESU) and equals approximately 8.988 × 10¹¹ Ohms. AbOhm belongs to the CGS electromagnetic system (EMU) and equals 10⁻⁹ Ohms. Both are obsolete units from the centimeter-gram-second system, largely replaced by the SI Ohm. The ratio between them is exactly c² (speed of light squared).
For most metals, resistance increases with temperature according to Rₜ = R₀(1 + αΔT), where α is the temperature coefficient. For copper, α ≈ 0.00393/°C. For semiconductors and insulators, resistance typically decreases with temperature (negative temperature coefficient). Superconductors exhibit zero resistance below their critical temperature.
Conductance (G) is the reciprocal of resistance: G = 1/R. It is measured in Siemens (S), formerly called mhos (℧). A high resistance means low conductance and vice versa. For example, a 100 Ω resistor has a conductance of 0.01 S (10 mS). Conductance is useful when analyzing parallel circuits.
Common resistance values in electronics:
- PCB traces: milliohms (mΩ)
- LED current limiting: 100 Ω to 1 kΩ
- Pull-up/pull-down resistors: 4.7 kΩ to 10 kΩ
- Audio circuits: 10 kΩ to 100 kΩ
- High-impedance inputs: 1 MΩ to 10 MΩ
- Insulation resistance: 100 MΩ to 1 GΩ+
Our converter uses conversion factors from NIST, BIPM, and the International Electrotechnical Commission (IEC). Results are accurate to 10 significant digits. For the Quantized Hall Resistance, we use the 2018 CODATA recommended value of 25,812.8074593045 Ω. This precision is suitable for engineering, scientific research, and metrology applications.
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