Electrical Resistance Converter

Convert between electrical resistance units including ohms (Ω), kiloohms (kΩ), megaohms (MΩ), and more.

---

---

Common Resistor Values (E12 Series)

Common Resistance Conversions

Standard Resistor Values (E12 Series)

12 values per decade with ~10% spacing:

• Base values: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82
• Example decade (kΩ): 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2
• Next decade: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 (repeat with 10× multiplier)

E-Series Standards

• E6: 6 values per decade (20% tolerance) - 10, 15, 22, 33, 47, 68
• E12: 12 values per decade (10% tolerance) - most common
• E24: 24 values per decade (5% tolerance)
• E48: 48 values per decade (2% tolerance)
• E96: 96 values per decade (1% tolerance) - precision resistors
• E192: 192 values per decade (0.5% tolerance) - high precision

Typical Resistance Ranges by Application

---

About Electrical Resistance

Electrical resistance is the opposition to the flow of electric current through a conductor. It converts electrical energy into heat and is fundamental to all electronic circuits.

The Ohm (Ω)

The ohm (Ω) is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm. Since 2019, it is defined using the quantum Hall effect and fundamental constants:

1 Ω = 1 V / 1 A

One ohm is the resistance between two points when a potential difference of one volt produces a current of one ampere.

Ohm's Law

The fundamental relationship between voltage, current, and resistance:

V = I × R

Where:

• V = Voltage (volts)
• I = Current (amperes)
• R = Resistance (ohms)

Rearranged forms:

• I = V / R (Current = Voltage / Resistance)
• R = V / I (Resistance = Voltage / Current)

Power Dissipation

Resistors convert electrical energy to heat. Power dissipated:

P = I² × R = V² / R = V × I

Where P = Power (watts). Resistors are rated by power: 1/8 W, 1/4 W, 1/2 W, 1 W, 2 W, etc.

Example: 100 Ω resistor with 5V across it dissipates: P = 5² / 100 = 0.25 W (1/4 watt resistor needed)

Series and Parallel Resistors

Series: Total resistance is the sum

R_total = R₁ + R₂ + R₃ + ...

Parallel: Reciprocal of total is sum of reciprocals

1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ...

Two resistors in parallel: R_total = (R₁ × R₂) / (R₁ + R₂)

Resistor Color Code

Standard 4-band or 5-band color code indicates resistance value:

• Band 1: First digit
• Band 2: Second digit
• Band 3 (multiplier): Number of zeros
• Band 4 (tolerance): Gold (5%), Silver (10%), None (20%)

Color values: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9

Example: Brown-Black-Red-Gold = 10 × 10² = 1000 Ω = 1 kΩ ±5%

Resistance and Temperature

Resistance varies with temperature:

• Positive Temperature Coefficient (PTC): Resistance increases with temperature (most metals)
• Negative Temperature Coefficient (NTC): Resistance decreases with temperature (thermistors, semiconductors)
• Temperature coefficient: Typically ±50 to ±200 ppm/°C for precision resistors

Resistor Types

• Carbon composition: Cheap, noisy, 5-20% tolerance
• Carbon film: Better stability, 1-5% tolerance
• Metal film: Precision, 0.1-1% tolerance, low noise
• Wire-wound: High power (1-100W), low resistance values
• Thick/Thin film (SMD): Surface mount, 0.1-5% tolerance
• Variable (potentiometer): Adjustable resistance

CGS Units

• Abohm (abΩ): CGS electromagnetic unit = 10⁻⁹ Ω (1 nanoohm)
• Statohm (statΩ): CGS electrostatic unit ≈ 8.988×10¹¹ Ω

These units are obsolete, replaced by SI ohms.

Conductance

The reciprocal of resistance is conductance (G), measured in siemens (S):

G = 1 / R (siemens = 1/ohm = mho)

Higher conductance means lower resistance and easier current flow.

Practical Applications

• Current limiting: Protect LEDs and circuits from overcurrent
• Voltage division: Create reference voltages
• Pull-up/pull-down: Set default logic levels in digital circuits
• Biasing: Set operating points for transistors and amplifiers
• Filtering: RC/RL filters in combination with capacitors/inductors
• Sensing: Temperature (thermistors), light (photoresistors), strain gauges
• Impedance matching: Maximize power transfer

Measurement

• Multimeter: Direct resistance measurement (Ω mode)
• Four-wire measurement: Eliminates lead resistance for low values (< 1 Ω)
• Megohmmeter: High-voltage testing for insulation resistance (GΩ range)

---

Feedback