Series and parallel resistance calculator

Two resistors in series and parallel; ideal components.

circuits-resistor-network.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	seriesohm	parallelohm	parallelPowerW
	3000	666.667	0.216
	2800	571.429	0.252

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

parallel power budget0.22 W✓ passes

BASELINE INPUTS

resistorA1000 ohmresistorB2000 ohmvoltage12 V

CALCULATED

series3000 ohm

parallel666.67 ohm

parallelPower0.216 W

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Series and parallel resistance
# Scope: Two resistors in series and parallel; ideal components.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

resistorA = 1000 ohm
resistorB = 2000 ohm
voltage = 12 V

series := resistorA+resistorB [ohm]
parallel := resistorA*resistorB/(resistorA+resistorB) [ohm]
parallelPower := voltage^2/parallel [W]

check parallel power budget: parallelPower <= 0.25 W

scenario alternative: resistorA = 800 ohm

Calculated from your source · not saved

Baseline · Baseline

parallel power budget0.22 W ✓ passes

alternative · alternative

parallel power budget0.25 W × fails

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

series: series = resistorA+resistorB [ohm]
parallel: parallel = resistorA*resistorB/(resistorA+resistorB) [ohm]
parallel power: parallelPower = voltage^2/parallel [W]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

resistor a: 1000 ohm
resistor b: 2000 ohm
voltage: 12 V

Calculated

series: 3000 ohm
parallel: 666.667 ohm
parallel power: 0.216 W

Assumptions and limits

Two resistors in series and parallel; ideal components.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Series and parallel resistance. Inputs: resistor values; connection pattern. Outputs: equivalent resistance; tolerance bounds. Model scope: Ideal or parameterized lumped components. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: resistor values, connection pattern
Outputs: equivalent resistance, tolerance bounds
Modes: calculate, compare, sweep
Drawing: Schematic and waveform

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS