Toolarithm

Physics Calculator

Ohm's Law Calculator

Use current and resistance to calculate voltage with V = IR. The result also shows power and conversion rows for milliamps, kilohms, millivolts, and milliwatts.

Live calculator

Current and resistance

Voltage

9.4 V

Current

0.02 A

Resistance

470 ohm

Power

0.188 W

Voltage in mV9,400 mV
Current in mA20 mA
Resistance in kohm0.47 kohm
Power in mW188 mW

Formula

V = I x R

Units

A, mA, ohm, kohm

Also shows

P = VI

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What Can You Create?

Check basic circuit relationships without hiding units

Voltage from current and resistance

Calculate potential difference using the standard V = I x R relationship.

Power side check

See P = VI beside the voltage result so circuit examples can be cross-checked.

Common electrical units

Review mV, V, mA, A, ohm, kohm, mW, and W conversions in the same result.

Formula

Ohm's law formulas used on this page

Ohm's law relates voltage, current, and resistance for simple resistive circuit examples. Power is calculated from voltage and current.

Working formulas

Ohm's law

V = I x R

Voltage equals current multiplied by resistance.

Current form

I = V / R

Current can be solved when voltage and resistance are known.

Electrical power

P = V x I

Power is shown as a related circuit check.

Symbols

V - voltage
Electric potential difference in volts.
I - current
Electric current in amperes.
R - resistance
Electrical resistance in ohms.
P - power
Electrical power in watts.
Read the Result

Interpret this calculation before using it

Ohm's law relates voltage across, current through, and resistance of the same element at an operating point. Solving V = IR is straightforward only after units and prefixes are consistent. The calculated power is a consequence of that idealized point and should not be confused with a safe component rating.

Worked example

With 12 V across a 4 ohm resistor, current is I = 12 / 4 = 3 A. The ideal electrical power is P = VI = 36 W, which also equals I^2R = 3^2 x 4. Those matching results verify the arithmetic, but they do not mean an arbitrary 4 ohm resistor can safely dissipate 36 W.

Assumptions to keep

  • Voltage, current, and resistance describe the same component under a steady, compatible operating condition.
  • Resistance is treated as constant, even though many materials and devices change with temperature or voltage.
  • The simple model omits source resistance, wiring loss, tolerance, transients, AC reactance, and measurement loading.

Limits of this result

Diodes, lamps, semiconductors, batteries, and reactive AC circuits may not follow a constant-resistance relationship. Electrical safety and component selection require ratings, thermal design, insulation, fault analysis, and applicable standards. Use the calculator for educational checks, never to approve work on energized equipment.

Useful next step: Electrical Power Calculator — Compare equivalent power formulas after the voltage-current-resistance relationship has been established.

Factual reference:OpenStax University Physics Volume 2
Why Users Love This Tool

Circuit output with conversion rows attached

Formula-first circuit checks

  • The calculator normalizes current and resistance before calculating voltage.
  • Power is displayed so the same inputs can be checked against P = VI.
  • Conversion rows show mV, mA, kohm, and mW without changing the formula.
  • Copy and print controls support worksheet answers and quick circuit notes.

Educational scope

  • The page is written for physics and electronics arithmetic, not electrical safety advice.
  • FAQ answers explain unit consistency, resistance meaning, and power checks.
  • Related links connect Ohm's law to electrical power and the physics worksheets guide.
  • The formula section defines each symbol before users rely on the result.
Perfect For

Ohm's law support for physics and electronics practice

Students

Check homework arithmetic while keeping SI conversions and formula variables visible.

Teachers

Create worksheet examples with formulas, units, and result summaries that print cleanly.

Formula reviewers

Audit values across common unit systems before comparing physics examples.

How It Works

How it works in three quick steps.

1

Enter current

Type the circuit current and choose amperes or milliamperes.

2

Enter resistance

Type the resistance and choose ohms, kilohms, or megohms.

3

Read voltage and power

Use the voltage result and power row to check the circuit relationship.

Download & Print

Save or print an Ohm's law result

Copy the result

Copy the formula result and normalized SI values into notes, worksheets, or lesson drafts.

Print the calculator

Print inputs, outputs, formula notes, FAQ answers, and related physics links.

Compare examples

Change one variable at a time to see how unit conversions affect the final value.

FAQ

Frequently Asked Questions

What does Ohm's law calculate?
Ohm's law relates voltage, current, and resistance in a simple resistive circuit. This page starts with current and resistance, then calculates voltage using V = I x R. It also calculates power with P = V x I so the same example can be checked from another circuit relationship.
Why does the calculator convert milliamps to amps?
The SI form of Ohm's law uses amperes, volts, and ohms. If current is entered in milliamps, the calculator converts it to amperes before multiplying by resistance. This prevents a common worksheet mistake where a value like 20 mA is treated as 20 A.
Can this calculator solve for current or resistance?
This page focuses on voltage from current and resistance, but the formula block shows the related forms I = V / R and R = V / I. The result table is still useful for checking unit scale. Future physics releases can add a mode selector for solving any one missing circuit variable.
Is electrical power the same as voltage?
No. Voltage is electric potential difference, while power is the rate of energy transfer. A circuit can have the same voltage but different power depending on current. The calculator shows power because it is often the next worksheet check after using Ohm's law.
Can I use this for real electrical safety decisions?
No. This calculator is an educational arithmetic tool. Real electrical work involves safety codes, component ratings, heat, insulation, wiring, fault conditions, and professional review. Use this page for physics examples and formula checks, not for approving a live circuit design.
About This Tool

Why Ohm's law pages need explicit unit conversion

Ohm's law is simple, but unit mistakes can make the answer unusable. Current may be given in milliamps, resistance in kilohms, and the expected answer in volts or millivolts. Toolarithm's Ohm's Law Calculator normalizes the inputs to amperes and ohms before applying V = I x R. The conversion rows are shown beside the result so the scale can be audited without repeating the calculation manually.

The page is deliberately scoped to education. It helps students and teachers check the mathematical relationship between current, resistance, voltage, and power. It does not replace electrical safety practice, component datasheets, circuit simulation, or professional engineering review. The related physics tools extend the same pattern into electrical power, energy, and motion formulas.

Editorial Transparency

Who maintains this page

Ownership and review

Written and maintained by the Toolarithm editorial team. No review date is shown without a maintained editorial record. No independent professional review is claimed.

Methodology

The method identifies the governing relationship, units, significant assumptions, and educational scope. SI terminology is checked against the BIPM reference.

Read the editorial methodology

Dates and sources

Review dates change only after a substantive method or content check.

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