SettingsSettings for this calculationUS
The voltage across the circuit or component.
Known from your power source (e.g. 12V for landscape lighting, 120V for standard outlets).
The resistance of the circuit or component, in ohms.
Found on a component's spec sheet, or calculated from wire gauge and length.
Current
3 A (current)
- Power
- 36 W
- Voltage
- 12 V
- Resistance
- 4 Ω
They open the calculator with your figures already in it
Ohm's Law Calculator: 3 A (current) — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Ohm's Law: V = I x R. Power equation: P = V x I. Both are exact, universal physics relationships, not rules of thumb.
Inputs used
- Voltage (V)
- 12
- Resistance (Ω)
- 4
Intermediate steps
- Power
- 36 W
- Voltage
- 12 V
- Resistance
- 4 Ω
What this calculation does not cover
- This is not a load calculation and not a circuit design. It returns the current a fixed resistance draws at a given voltage, and says nothing about conductor ampacity, derating for ambient temperature or conduit fill, overcurrent device sizing, or whether the circuit is compliant.
- The model assumes a purely resistive load. On an AC circuit with motors, transformers, LED drivers or switch-mode supplies the current is set by impedance rather than plain resistance, and the power figure is apparent power in volt-amps, not watts, wherever the power factor is below 1.
- Resistance is taken as a fixed number. Conductor, element and filament resistance rise with temperature and terminations add their own, so a cold ohmmeter reading understates the operating resistance and the current shown will run high against what the circuit actually draws hot.
- Nothing is subtracted for the supply run. The voltage you enter is assumed to appear across the resistance itself, so on a long circuit the load sees less than that and draws proportionally less current than the figure here.
- The calculator prints whatever the arithmetic gives, including the fault-level current a very low resistance produces at mains voltage. It is not a short-circuit, interrupting-rating or arc-flash study, and it does not check that the current or power it reports is survivable for the conductors, the device or the person working on it.
Add the equipment this sizes
This result is a specification — 3 A (current) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Ohm's Law: V = I x R. Power equation: P = V x I. Both are exact, universal physics relationships, not rules of thumb.
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