Resistor Calculator.
Equivalent Resistance Calculator: Series, Parallel, Ohm's Law & Applications
Learn how to calculate equivalent resistance, apply Ohm's Law, understand formulas, and manage heat dissipation efficiently.
How to Calculate Equivalent Resistance
In a circuit, the equivalent resistance lets you replace multiple resistors with a single one, maintaining the same electrical effect. There are two main cases:
Series Resistors
Formula: R_eq = R1 + R2 + R3 + ... + Rn
The current is the same through each resistor, but the voltage is divided.
Parallel Resistors
Formula: 1 / R_eq = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn
Voltage remains the same across each resistor, but the current is divided.
Ohm's Law
Ohm's Law is essential: U = R × I
It links voltage (U), current (I), and resistance (R).
- U: Voltage (volts)
- R: Resistance (ohms)
- I: Current (amperes)
Power and Heat Dissipation
Resistors generate heat according to: P = U × I or P = I² × R
Always choose a resistor with a sufficient power rating.
Using Parallel Resistors to Dissipate More Heat
When the power requirement exceeds a single resistor’s capacity, you can use multiple resistors in parallel:
- The current is shared, so each resistor heats less
- Better thermal distribution
- More reliable and cost-effective solution
Example: Need 100 Ω at 2 W, but only have 200 Ω 1 W resistors.
Use two in parallel: R_eq = 1 / (1/200 + 1/200) = 100 Ω
Each one safely dissipates 1 W.
Practical Applications
Current Limiting for LEDs
LEDs need a series resistor to limit current. Example: 5V supply – 2V LED = 3V across resistor → 3V / 0.02A = 150 Ω.
Voltage Divider
Two resistors in series can create an intermediate voltage, often used with sensors and microcontrollers.
Thermal Calculation
Always check power dissipation: if a resistor needs to handle 0.5 W, use at least a 1 W-rated component for safety.
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Resistor Color Code → Value:
Instantly find the resistor value from its color bands.
Value → Resistor Color Code:
Get the color bands for any resistor value.
Resistance serie/parallel:
Combine resistors and get the total resistance.
Resistivity:
Compute resistance based on material and wire dimensions.
Voltage divider:
Calculate output voltage in a classic divider setup.
Ohm’s Law:
Easily relate voltage, current,power and resistance.
Voltage Drop in a Conductor:
Find how much voltage is lost along a wire.
LED Resistor Calculator:
Find the right resistor for your LED safely.
Series/Parallel Capacitors:
Combine capacitors and get the total capacitance.
Ceramic Capacitor Value:
Decode the value printed on ceramic caps.
Capacitor Design Tool:
Design a capacitor based on specs and materials.
Delta → Star Converter:
Convert a triangle connection to a star.
Star → Delta Converter:
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Inductor Design Tool:
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Series/Parallel Inductors:
Combine inductors and get the total inductance.
High/low pass filter:
compute cuttoff frequency/decibel & out voltage.
Impedance L,C:
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Impedance RLC:
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Calculate voltage, turns ratio, for transformers.
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RC Time Constant:
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Frequency / Wavelength:
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RMS calculator:
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Decibel calculator:
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Components,Module & IC.
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inductor.
optocoupler.
regulator.
hall effect sensor.
diac.
transformer.
ceramic resonator.
relay.
fuse.
micro electret.
quartz.
NE555.
TL494.
TDA2822.
LM386.
TDA3886.
serie 74HCXX.
OP amp.
Arduino.
