Resistance Calculator
Calculate electrical resistance using Ohm's Law and power formulas
Electrical Parameters
How to Use This Calculator
Choose Calculation Type
Select between Ohm's Law calculations (V = I × R), Power Law calculations (P = V × I), or Color Bands Reading to calculate resistance from resistor color codes.
Enter Known Values
Input at least 2 known electrical parameters. The calculator will automatically compute the missing values when you finish entering data.
Read Color Bands
For Color Bands Reading, select 4-band or 5-band resistor type, then choose the colors for each band. The calculator will show the resistance value and tolerance.
Review Results
Check all calculated values including voltage, current, resistance, power, and additional information like conductance and resistor color codes.
Use Additional Features
View calculation history, share results, and get suggestions for component power ratings and tolerances.
Understand Color Codes
For resistance values, see the corresponding resistor color code bands to help identify physical resistor components. You can also use the Color Bands Reading mode to calculate resistance from color bands.
Apply Safety Margins
Note the suggested power rating which includes a safety margin. Always use components rated above the calculated power dissipation.
Electrical Engineering Tips
Always use components with power ratings at least 2x the calculated power dissipation for safety and longevity.
Remember that Ohm's Law applies to resistive circuits. Reactive components (inductors, capacitors) require different calculations.
Conductance is the inverse of resistance. Higher conductance means lower resistance and better current flow.
Standard resistor values follow E-series (E12, E24, etc.). Your calculated value may need to be rounded to available values.
Temperature affects resistance. Most resistors have temperature coefficients that change their value with heat.
For precision applications, consider resistor tolerance. 1% resistors are more accurate than 5% resistors.
In parallel circuits, total resistance is always less than the smallest individual resistance.
In series circuits, total resistance equals the sum of all individual resistances.
Power dissipation creates heat. Ensure adequate cooling for high-power applications.
Use proper wire gauge for the calculated current to prevent voltage drop and heating.
Resistor color bands follow a standard code: 0=Black, 1=Brown, 2=Red, 3=Orange, 4=Yellow, 5=Green, 6=Blue, 7=Violet, 8=Gray, 9=White.
Gold and Silver bands are used for multipliers (0.1 and 0.01) and tolerances (±5% and ±10%).
Always read resistor color bands from left to right, with the tolerance band usually separated by a gap.
For 5-band resistors, the first three bands are digits, the fourth is multiplier, and the fifth is tolerance.