Series and Parallel Resistor, Capacitor and Inductor Calculator

Combine up to four resistors, inductors or capacitors in series and in parallel, and see the current and voltage across each part.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Resistors and inductors add in series. In parallel the reciprocal of the total is the sum of the reciprocals. Capacitors are the other way round: they add in parallel and combine by reciprocals in series.

In a series circuit the same current flows through every part and the voltage splits in proportion to the values. In a parallel circuit the same voltage is across every branch and the current splits.

Formulas used

  • R_s = R_1 + R_2 + R_3
  • \dfrac{1}{R_p} = \dfrac{1}{R_1}+\dfrac{1}{R_2}+\dfrac{1}{R_3}

Worked example

With the default numbers in the calculator above:

  1. Series total: 650.00
  2. Parallel total: 56.90
  3. Series: the one current in every part, in the unit of voltage over value: 0.0185
  4. Series: the voltage across each part: 1.85, 4.06, 6.09 (adds to 12.00)
  5. Parallel: the current in each branch (same voltage across all): 0.12, 0.0545, 0.0364 (total 0.21)

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

Why is the parallel total smaller than any single resistor?

Each extra branch gives the current another path, so the total opposition falls.

Do coils combine like resistors?

Yes, when they do not share a magnetic field. Capacitors combine the opposite way.

Related calculators

Further reading: Standard electrical engineering texts (series and parallel circuits).

Need a calculator we do not have?

Tell us what you would like to calculate. We read every request and build the most asked-for ones.

We store your request (and your email if you give it) to decide what to build. We do not store the numbers you type into calculators.

Embed this calculator on your own page

Copy this code into your page. The calculator runs inside the frame and links back to Drafting Central.

Need this drawn, designed or checked?

Drafting Central is a mechanical engineering and drafting business in Burleigh Waters on the Gold Coast. A calculator gives you the numbers; we can turn them into drawings and designs.

Need help with a real project?

Talk to Drafting Central →

← All engineering calculators