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Electrical calculator

Current Divider Calculator

Split a total current between two parallel resistors: I1 = It·R2/(R1+R2), I2 = It·R1/(R1+R2). Runs locally in your browser.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance
Input interpretation
Enter values to calculate.
Result
—
Assurance
Engineering
Declared partition coverage
PASS · 8/8 declared partitions (from-It-R, from-I1-R, from-I2-R, from-It-I1-R1, from-It-I1-R2, underdetermined-currents, inverse-endpoint, invalid-domain) · Matrix
Known limitations
  • Exactly two ideal resistive parallel branches; no additional branch or load. Currents are non-negative magnitudes.
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
Two-branch parallel current divider currents and node voltage.
Scope
Exactly two ideal resistive parallel branches; no additional branch or load
Verification
Engine tested · Source checked · v1.0.2 · CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance· View Manifest · CVP overview · Specification
Versions
Calculation 1.0.2 · CVP protocol 1.0.0-proposed · Evidence 2026-09-14.inverse-endpoints-schema
Verification revision
2026-09-14.inverse-endpoints-schema · 2/2 property · digest 5836a820dfe6
Legacy regression
23/23 tests · Production surface contract 4/4
Trust layers
Verification VERIFIED · Production CURRENT · overall VERIFIED
Reference
O1 model · O2 expected_values · O2 numerical_behavior
Interfaces
PASS · UI (SSR) / REST / MCP — ui-ssr is query-result HTML, not a live browser session.
Supplemental domain review
Internal · Pass · electrical-engineer
Named expert review
Not performed
CVP suite
5/5 golden · 14/14 CVP boundary · 20/20 invalid · 2/2 property · 3/3 metamorphic · 1/1 cross-interface · 4/4 CVP contract · Manifest
Sources
Sources
Methods
  • Kirchhoff's current law (KCL): I1 + I2 = It
  • Ohm's law: V = I1·R1 = I2·R2
Evidence
5 legacy golden · 12 legacy boundary · legacy regression suite · 5/5 oracle-backed golden · 20/20 invalid · Artifact integrity PASS · CalculatorX electrical review
This calculator CURRENT · Public schema 1.0.2 matches · Semantic contract ✓ · Production attested · Public/cache ✓ · Origin ✓
Semantic contract
PASS
Full verification

Manifest identity, reference classes, interfaces, suite, and production records.

Formulas

Core equations used by this calculator.

Branch current I1I1 = It·R2/(R1+R2)
Branch current I2I2 = It·R1/(R1+R2)
iIdeal DC resistors. Web calculator: enter It, R1, and R2. API additionally solves selected inverse combinations (not arbitrary any-three; It+I1+I2 is underdetermined).

How to use

1

Enter total current It, R1, and R2

The web calculator computes I1, I2, and branch voltage V. Currents are non-negative magnitudes; resistances must be > 0.

2

Confirm the two-resistor parallel split

I1 = It·R2/(R1+R2) and I2 = It·R1/(R1+R2). I1 uses R2 because the larger share of current goes through the smaller resistance.

3

Read I1, I2, and the common branch voltage

Both branches see the same V = I1·R1 = I2·R2. REST/MCP can also solve selected missing-value combinations.

Example calculations

Common configurations with formula and result.

ϟ

30 mA into 100∥200

It=0.03 A · R1=100 Ω · R2=200 Ω

I1 = It·R2/(R1+R2); I2 = It·R1/(R1+R2)
I1=0.02 A · I2=0.01 A · V=2 V

Current Divider calculator specification

Version 1.0.2 · Engine tested · Supplemental domain review · Internal · 2026-09-14

Calculation status

Review policy · Evidence · Reviewed by CalculatorX electrical review (electrical-engineer)

Definition
In a two-resistor parallel current divider, branch current is inversely proportional to resistance: I1 = It·R2/(R1+R2), I2 = It·R1/(R1+R2).
What it calculates
Two-branch parallel current divider currents and node voltage.
Inputs
  • Web: It, R1, R2. API: a solvable combination of It, R1, R2, I1, I2 (R>0; currents are non-negative magnitudes)
Outputs
  • It
  • R1
  • R2
  • I1
  • I2
  • V
Formula
I1 = It·R2/(R1+R2); I2 = It·R1/(R1+R2)
Assumptions
  • Exactly two ideal resistive parallel branches; no additional branch or load
  • DC / resistive; currents entered as non-negative magnitudes
Units
  • A, Ω, V
Boundary conditions
  • <3 inputs → NEEDS_THREE_INPUTS
  • R≤0 → VALUE_MUST_BE_POSITIVE
  • It+I1+I2 → UNSUPPORTED_COMBINATION (underdetermined)
  • It+I1+R inverse: I1=0 or I1=It → CURRENT_SPLIT_INVALID (no finite R>0)
  • It=0 and I1=0 with R1 or R2 → UNSUPPORTED_COMBINATION (degenerate)
Example
It=30 mA, 100∥200 → I1=20 mA, I2=10 mA, V=2 V
Validation cases

1 published on this page · 23/23 tests · Production surface contract 4/4 · View evidence

  • It=0.03,R1=100,R2=200 → I1=0.02,I2=0.01,V=2
Methods
  • Kirchhoff's current law (KCL): I1 + I2 = It
  • Ohm's law: V = I1·R1 = I2·R2
Sources
  • IEC 60050 — International Electrotechnical Vocabulary — Kirchhoff law for nodes (IEV 131-15-09) · accessed 2026-09-12
    Supports: Algebraic sum of currents at a node is zero; I1 + I2 = It for two parallel branches
  • IEC 60050 — International Electrotechnical Vocabulary — Resistance (IEV 131-12-04) · accessed 2026-09-12
    Supports: R = u/I on each branch; common node voltage V = I1·R1 = I2·R2
  • Horowitz & Hill — The Art of Electronics — 3rd ed., Cambridge University Press, 2015 — Chapter 1 Foundations, current dividers · 2015
    Supports: Two-branch inverse-R current split
Last reviewed
2026-09-14
Reviewed by
CalculatorX electrical review (electrical-engineer)
Calculation version
1.0.2

Background

Interpretation and common distinctions.

Compute a two-resistor current divider.

Default: It=30 mA · 100 Ω ∥ 200 Ω → I1=0.02 A, I2=0.01 A, V=2 V.

The web form takes It, R1, and R2. REST / MCP additionally support selected inverse-solving combinations; they do not accept arbitrary any-three tuples. It + I1 + I2 is underdetermined.

Supported and not supported

Supported — Two ideal resistive parallel branches · API electrical.current_divider

  • Web: It, R1, R2 → I1, I2, V
  • API: It+R1+R2; R1+R2+I1; R1+R2+I2; It+I1+R1; It+I1+R2

Not supported — N>2 branches, AC impedance networks, additional parallel load/current path, signed reference-direction currents, It+I1+I2 (underdetermined)

Agent / API notes

Capability id: electrical.current_divider · tool id: current-divider · pin 1.0.2.

Errors: NEEDS_THREE_INPUTS, VALUE_MUST_BE_POSITIVE, VALUE_MUST_BE_NON_NEGATIVE, UNSUPPORTED_COMBINATION, CURRENT_SPLIT_INVALID. Inverse It+I1+R1/R2 needs 0 < I1 < It for a finite R>0; It=I1=0 is underdetermined.

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Frequently asked questions

Key distinctions behind the calculation.

Why does more current go through the smaller resistor?

Branch current is inversely proportional to resistance — the lower-R path takes more of It. That is why I1 = It·R2/(R1+R2) multiplies by the other branch's resistance.

Is It + I1 + I2 enough to find R1 and R2?

No. Those three currents only fix the resistance ratio (R2/R1 = I1/I2). Absolute ohm values are underdetermined. The web calculator takes It, R1, and R2. The API solves only selected uniquely determined combinations (It+R1+R2, R1+R2+I1 or I2, It+I1+R1 or R2).

Fewer than three inputs?

API returns NEEDS_THREE_INPUTS.