Resistor Code Tools
Color band decoder
SMD code and E-series helper
Calculation History
Recent calculations appear here.
Formula Used
Series circuit
Req = R1 + R2 + ... + Rn
Parallel circuit
1/Req = 1/R1 + 1/R2 + ... + 1/Rn
Two parallel resistors
Req = (R1 × R2) / (R1 + R2)
Temperature adjustment
R(T) = Rref[1 + α(T − Tref)]
Current and power
I = V/Req, P = V²/Req
Conductance
G = 1/Req
How to Use This Calculator
- Select the circuit arrangement you want to analyze.
- Add resistor values and choose each matching unit.
- Enter tolerance and temperature data when available.
- Set open or short conditions for fault simulation.
- Enter the supply voltage for current and power results.
- Use labels inside mixed S(...) and P(...) expressions.
- Click calculate to view detailed electrical results.
- Copy, print, or export the completed calculation.
Example Data
| Example | Inputs | Method | Equivalent resistance |
|---|---|---|---|
| Series network | 100 Ω, 220 Ω, 330 Ω | Add all values | 650 Ω |
| Parallel network | 100 Ω, 200 Ω | Product over sum | 66.667 Ω |
| Identical parallel | Four 1 kΩ resistors | R ÷ n | 250 Ω |
| Mixed network | S(100,P(200,300),50) | Reduce inner group first | 270 Ω |
Frequently Asked Questions
What is equivalent resistance?
Equivalent resistance replaces a resistor network with one resistance. It preserves the same terminal current-voltage behavior.
How are series resistors calculated?
Add every series resistance directly. Series current remains equal through each resistor.
How are parallel resistors calculated?
Add the reciprocal of each resistance. Then take the reciprocal of that sum.
Can equivalent resistance exceed every branch resistor?
It can in series circuits. A parallel result stays below the smallest active branch.
What does an open resistor do?
An open resistor blocks its path completely. A series open makes the full circuit open.
What does a shorted resistor do?
A short has nearly zero resistance. A parallel short drives equivalent resistance toward zero.
Why include resistor tolerance?
Real resistors vary from nominal values. Tolerance estimates possible minimum and maximum results.
What is temperature coefficient?
It describes resistance change per temperature degree. The usual unit is parts per million.
Can this calculator solve bridge circuits?
Yes. Bridge mode uses nodal analysis for five-resistor Wheatstone networks.