Electrical calculator
Parallel Resistor Calculator
Calculate equivalent resistance of resistors in parallel.
About the parallel resistor calculator
The parallel resistor calculator finds the equivalent resistance of 2-4 resistors connected in parallel.
How to use this calculator
- 1
Enter resistor values
Enter at least 2 resistor values (R3 and R4 are optional).
- 2
View results
See the equivalent resistance.
How the calculation works
1/Rtotal = 1/R1 + 1/R2 + 1/R3 + 1/R4. The equivalent is always less than the smallest resistor.
Example: 100Ω || 200Ω = 66.67Ω.
Safety first
These calculators provide estimates based on standard formulas and NEC guidelines. Always verify results with a licensed electrician before making installations. Electrical work can be dangerous — never work on live circuits, and always follow local building codes and regulations.
Understanding electrical units
Voltage (V) is electrical pressure, current (A) is flow rate, resistance (Ω) opposes flow, and power (W) is the rate of energy use. Ohm's law (V = I × R) relates the first three, while power formulas (P = VI, P = I²R) connect all four. Understanding these relationships is key to safe electrical design.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about parallel resistor calculator
How accurate is the parallel resistor calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.