About

Why this site exists

Combining resistors, capacitors and inductors is first-year theory, but doing it quickly and correctly during real design work is more awkward than it should be.

The calculators already online share three problems. They only work forwards — enter every value, receive a total — when the question in practice is often the reverse: you know the total you need and one of the parts, and you want the other. They give a number with no working, so there is nothing to check. And they hand you a value like 3.197 kΩ without mentioning that you cannot buy it.

These tools address all three. They solve in both directions, they print the reduction step by step, and every answer arrives with the nearest preferred values and the error each one costs you.

What the tools do

• Series, parallel and mixed networks, for resistance, capacitance and inductance.
• Find the equivalent value of a network, or solve for one missing component from a known equivalent.
• Arbitrary nesting of series and parallel groups, drawn as a two-terminal schematic that updates as you edit.
• The nearest IEC 60063 preferred values for every result, with signed error and a note when your tolerance cannot actually reach the target. Resistors offer the full range of series; capacitors and inductors offer the coarser ones they are really made in.
• A step-by-step derivation you can copy straight into a design note.
• Undo and redo per calculator. Each one keeps its own network for the session, so opening another does not disturb the one you were working on.

How the results are verified

Every answer comes from a small solver written from first principles, not from a lookup table.

The reverse solve is exact rather than an iterative search. Series and parallel combination both preserve a linear-fractional form, so a network with one unknown collapses to four coefficients that can be inverted directly. The same coefficients give the range of totals the network can actually produce, which is why the tool can tell you that a target is unreachable instead of returning a wrong number.

Preferred-value matching compares ratios, not differences. The E-series is geometric, so the tipping point between two neighbours is their geometric mean — which is what "nearest preferred value" means, and what a subtraction-based search gets wrong.

The engine is covered by an automated test suite that checks it against closed-form textbook answers, including a brute-force sweep confirming the exact reverse solve matches simply trying values. Every worked example printed on this site is rebuilt with that same engine by a test, so the text and the calculator cannot drift apart.

What the tools assume

Being clear about limits is more useful than claiming there are none. These tools assume:

• Ideal components. Parasitic resistance, inductance and capacitance are not modelled.
• No mutual magnetic coupling between inductors. Coils placed close together on a board will not match the calculated value — the inductor pages explain why.
• Nominal values. Tolerance, temperature coefficient and ageing are not applied, though the pages explain how each affects a real design.
• Direct current, or a single frequency treated as a pure reactance. There is no frequency sweep and no transient analysis.
• Class-II ceramic capacitors are assumed at their marked value. In reality they lose capacitance under DC bias, sometimes severely; the parallel capacitance page covers this.

Privacy and cost

The calculators run entirely inside your browser. Nothing you type is transmitted, there is no account, and the tools keep working with the network disconnected.

The site is free, carries no adverts, and sets no cookies. It loads no fonts, scripts or trackers from any other company.

Corrections

If a result looks wrong, please say so. Tests only cover what someone thought to check, and a specific report is the most useful message you can send. The contact page explains what to include.