Electricity & Magnetism
Resistors in Parallel
Total resistance of resistors in parallel.
Variables
ReqΩ
Equivalent resistance
Total resistance
In SI units: kg·m²/(A²·s³)
Allowed values: 0 or more
R₁Ω
Resistance 1
First resistor
In SI units: kg·m²/(A²·s³)
Allowed values: 0 or more
R₂Ω
Resistance 2
Second resistor
In SI units: kg·m²/(A²·s³)
Allowed values: 0 or more
Derivation
Same voltage: I = I₁ + I₂ = V/R₁ + V/R₂.
Your notes
0/5000
Check value
Round inputs run through this page's calculator. Use it to test your own working or a rearranged form. It is a test case, not a real-world example.
- R₁ = 2 Ω (Resistance 1)
- R₂ = 3 Ω (Resistance 2)
Result: Req = 1.2 Ω
Where this formula is listed
- Electricity & Magnetism formulas, under Electric Circuits, alongside Electric Power, Electric Current, Resistance, Kirchhoff's Voltage Law and Kirchhoff's Current Law.
- In the electricity & magnetism list it comes after Resistors in Series and before Kirchhoff's Voltage Law.
- Electricity & Magnetism formula sheet, one of 48 formulas printed with symbol keys and SI units.
- The full formula index, grouped by category and topic.
Common questions
What is the Resistors in Parallel formula?
Resistors in Parallel is written 1/R_eq = 1/R₁ + 1/R₂ + ... Total resistance of resistors in parallel. It belongs to Electricity & Magnetism, under Electric Circuits.
What are the units in 1/R_eq = 1/R₁ + 1/R₂ + ...?
In SI units, R_e q is equivalent resistance, measured in kg·m²/(A²·s³); R₁ is resistance 1, measured in kg·m²/(A²·s³); R₂ is resistance 2, measured in kg·m²/(A²·s³).
How is the Resistors in Parallel formula derived?
Same voltage: I = I₁ + I₂ = V/R₁ + V/R₂. The result is 1/R_eq = 1/R₁ + 1/R₂ + ...