Ohm's Law / Power Wheel Calculator Skip to main content
Electrical Free Pro Features Available

Ohm's Law / Power Wheel Calculator

Solve voltage, current, resistance, and power for DC, single-phase AC, and three-phase AC circuits

Field guide: Ohm's Law, Watt's Law, and the AC Power Triangle

PREVIEW All Pro features are currently free for a limited time. No license key required.

Electrical
Pop Out

Electrical bench kit

Basic measurement and circuit-building products for voltage, current, and power work:

As an Amazon Associate, ToolGrit earns from qualifying purchases, at no extra cost to you. These are hand-picked suggestions; calculator results are not influenced by them.

Use this Ohm's Law and Watt's Law calculator to organize ideal DC arithmetic and simple RMS AC power-triangle prompts. It solves local formula fixtures for voltage, current, resistance, power, apparent power, reactive power, and power-factor angle while keeping the measurement, waveform, code, equipment, and safe-work boundaries visible.

The output is not an NEC calculation of record, conductor or breaker selection, equipment rating, troubleshooting signoff, capacitor-bank sizing decision, or energized-work instruction. Verify RMS measurements, three-phase balance, waveform distortion, selected equipment data, adopted code, AHJ requirements, NFPA 70E/OSHA controls, and qualified electrical review before design, installation, troubleshooting, or energized work.

Pro Tip: Keep the measurement basis beside the arithmetic. For AC screens, note whether voltage and current are true-RMS, whether three-phase values are line-to-line and line current, whether the load is balanced, and whether power factor is displacement or true power factor. Those details control whether the simple formula prompt is useful.

Review local motor FLA rows before source and AHJ checks

Motor FLA Lookup (NEC 430) →

Convert torque and horsepower as a unit prompt only

Torque to Horsepower Converter →

Check transformer fault-current assumptions before study review

Transformer Fault Current Calculator →

How It Works

  1. Select Circuit Mode

    Choose ideal DC, single-phase AC, or three-phase AC. The AC screens assume RMS voltage/current and a user-entered positive power factor.

  2. Enter Complete Values

    Enter positive numeric values for the selected formula path. Malformed or partial values are blocked rather than silently treated as valid readings.

  3. Review Source Boundaries

    Use the output as an arithmetic prompt, then resolve measurement, waveform, equipment, code, AHJ, and safe-work gaps before decision use.

Assumptions

  • DC mode uses ideal positive-scalar Ohm's Law and Watt's Law relationships.
  • Single-phase AC uses RMS voltage/current and a user-entered power factor.
  • Three-phase AC uses line-to-line voltage and line current for a balanced-load calculator.
  • Equivalent horsepower is a unit prompt only and does not verify motor efficiency or output rating.

Limitations

  • Does not determine conductor ampacity, voltage drop, OCPD, SCCR/AIC, equipment listing, or NEC compliance.
  • Does not model unbalanced three-phase loads, neutral current, harmonics, nonlinear loads, VFD behavior, or transients.
  • Does not verify meter calibration, waveform capture, motor nameplate data, utility billing, or capacitor-bank correction.
  • Does not provide NFPA 70E/OSHA safe-work controls, PPE, LOTO, arc-flash, shock, permit, inspection, AHJ, or qualified-review signoff.

References

  1. NIST-OHMS-LAW-AMPERE-PRESENT - NIST Ohm's Law and ampere context
  2. NIST-SP-330-SI-2019 and NIST-SP811-B8 - SI unit and conversion source context
  3. NFPA-70-2026 - NEC source pointer only; no protected table text reproduced
  4. NFPA-70E-2024-SOURCE and OSHA-1910-303-ELECTRICAL-SOURCE - electrical safety source pointers

Frequently Asked Questions

The simplified three-phase screen uses line-to-line voltage and line current for a balanced system. The square-root-of-three factor comes from that line-value relationship. Unbalance, harmonics, neutral current, VFD behavior, and actual metered demand require source data beyond this calculator.
VA or kVA is an important review quantity, but this app does not select transformers, generators, UPS equipment, conductors, breakers, or switchgear. Use selected equipment data, load study context, adopted code, AHJ requirements, and qualified review.
The simple DC relationship is an ideal resistance model. AC work often needs impedance, phase angle, waveform, harmonic, and measurement context. The AC mode is a local power-triangle prompt, not a full impedance or power-quality study.
No. It can organize measured values and formula prompts, but troubleshooting still needs calibrated instruments, selected equipment data, safe-work controls, LOTO or energized-work authorization, and qualified electrical review.
Disclaimer: This is a preliminary source-aware arithmetic screen only. It is not an NEC calculation of record, conductor or OCPD selection, equipment rating, troubleshooting signoff, capacitor-bank sizing decision, or energized-work procedure.

Guides for this job

Electrical

Ohm's Law, Watt's Law, and the AC Power Triangle

The 12 Ohm's Law and Watt's Law relationships explained for DC and AC circuits. Power factor, real vs apparent vs reactive power, and worked motor load examples.

Read Guide →
Electrical

Motor Circuit Source-Boundary Guide

Complete motor circuit design from FLA lookup through wire sizing, overload selection, and branch circuit protection per NEC 430. Worked 25 HP example.

Read Guide →
Electrical

Fault Current Analysis for Electrical Distribution

Why fault current matters, how transformer impedance affects AFC, and why equipment ratings and arc flash need formal study data.

Read Guide →
Electrical

Torque, Horsepower, and Power Transmission Fundamentals

The HP formula and where 5252 comes from. Torque vs speed, drivetrain efficiency, gearbox selection, motor speeds, and VFD vs gearbox decisions.

Read Guide →

More Electrical tools

Electrical Live

Can I Run This On That?

Check if your circuit breaker and wiring can handle a specific appliance. Enter breaker size, wire gauge, and load wattage for a pass/fail verdict based on NEC standards.

Launch Tool →
Electrical Live

Wire Sizing Calculator

Find the right AWG wire gauge for any electrical run. Enter amps, distance, and voltage to get NEC-compliant sizing with derating, voltage drop, and copper vs aluminum cost comparison.

Launch Tool →
Electrical Live

Generator Sizing Calculator

What size generator do you need? Add your appliances and loads to calculate total running watts and starting surge. Get a recommended generator size with built-in headroom.

Launch Tool →