Electrical reference chart
Ohm's Law Formula Chart
Use this Ohm's Law formula chart after the calculator result to document the solved variable, formula path, unit basis, and power cross-check.
Quick reference table
Ohm's Law connects voltage, current, and resistance with V = I x R. Power relationships add P = V x I, P = I^2 x R, and P = V^2 / R. Use this chart as the formula-selection worksheet, then use the calculator result when values, units, and notes need a repeatable record.
Ohm's Law formula selection
| Solve for | Use this formula | Known values needed |
|---|---|---|
| Voltage | V = I x R | Current and resistance |
| Current | I = V / R | Voltage and resistance |
| Resistance | R = V / I | Voltage and current |
| Power from voltage and current | P = V x I | Voltage and current |
| Power from current and resistance | P = I^2 x R | Current and resistance |
| Power from voltage and resistance | P = V^2 / R | Voltage and resistance |
Calculator result cross-checks
| Result shows | Check next | Why it matters |
|---|---|---|
| Current solved | Power should also match P = V x I | Confirms the current value was not entered with the wrong unit |
| Resistance solved | Confirm the value is ohms, not kilohms or milliohms | Prefix mistakes can change the answer by 1,000x |
| Power solved | Confirm whether the load is DC, resistive AC, or an AC load with power factor | Simple Ohm formulas are not a full AC power model |
| Very small or very large result | Recheck decimal placement and source units | Magnitude checks catch most formula-entry errors |
Ohm's Law search intent map
| If the search asks for | Use this chart for | Open the calculator when |
|---|---|---|
| Ohm's Law formula | Choosing the voltage, current, resistance, or power equation | Actual values need to be entered and checked with units |
| Voltage current resistance formula | Matching the known values to the unknown variable | The result should be saved with a project note or example |
| Watts volts amps relationship | Confirming whether the power relationship is P = V x I, I^2 x R, or V^2 / R | Power factor, phase, or AC equipment behavior changes the model |
| Resistance from watts and volts | Selecting the derived resistance formula before calculation | The load is not a simple resistive load or the result looks unusual |
How to use this chart
Choose the unknown variable
Start by identifying whether the result needs voltage, current, resistance, or power before selecting a formula.
Match known inputs
Use the formula row where the known voltage, current, resistance, or power values match the data you actually have.
Cross-check the result
After the calculator result, use an alternate power relationship or magnitude check to catch unit and decimal-place errors.
Formula basis
V = I x R, I = V / R, R = V / I, P = V x I, P = I^2 x R, and P = V^2 / R.
- V is voltage in volts.
- I is current in amperes.
- R is resistance in ohms.
- P is real power in watts for the selected circuit condition.
Worked examples
Find current from voltage and resistance
For 120 V across 24 ohms, I = 120 / 24 = 5 A. The matching power check is P = 120 x 5 = 600 W.
Find resistance from power and voltage
For a 240 V resistive load at 4,800 W, R = V^2 / P = 240^2 / 4,800 = 12 ohms before checking whether the load model really is resistive.
Related calculators
Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law and power formulas
Voltage Calculator
Compute circuit voltage for DC and AC resistive loads from current, resistance, or power using standard Ohm's Law relationships (V = I × R, V = P / I, V = √(P × R)).
Current Calculator
Calculate current, voltage, resistance, and power using core Ohm's Law relationships, optimized for current-focused workflows.
Resistance Calculator
Calculate series, parallel, and complex resistance networks with temperature effects
Power Calculator
Electrical power calculator for DC, single-phase AC, and balanced three-phase AC relationships between voltage, current, real power, apparent power, reactive power, and power factor.
Related charts
Amps to Watts Chart
Use this amps to watts chart: 12A at 120V = 1,440W; 24A at 480V 3-phase with 0.82 PF is about 16,360W.
Watts to Amps Chart
Use this watts to amps chart: 1,500W at 120V = 12.5A, 9 kW at 240V = 37.5A; compare 208V, 240V, 480V 3-phase and PF.
Energy and kWh Conversion Chart
Convert watts, Wh, and kWh: 1,200 W for 3 hours is 3.6 kWh before rate, billing period, duty cycle, or cost checks.
Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.