1Find voltage: 2A through 6Ω
Inputs
Current2 A
Resistance6 Ω
Result
Voltage12.000 V
Power24.000 W
V = I × R = 2 × 6 = 12V. P = V × I = 12 × 2 = 24W.
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Ohm's Law Calculator
Voltage
12.000 V
V
12.000 V
P
24.000 W
Voltage
12.000 V
Voltage
12.000 V
Current
2.000 A
Resistance
6.000 Ω
Power
24.000 W
What You'll Need
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Digital Multimeter Voltmeter Battery Voltage Multi Tester Continuity Ohm Volt Amp DC AC Current Resistance Diodes 2000 Counts Electrical Test Meter with Leads Backlight LCD Display
$9.98
View on AmazonAstroAI Digital Multimeter Tester 2000 Counts with DC AC Voltmeter and Ohm Volt Amp Meter; Measures Voltage, Current, Resistance, Continuity and Diode, Blue
$14.59
View on AmazonKAIWEETS Electrical Test Kit KIT01, Digital Multimeter, Smart Non-Contact Voltage Tester & GFCI Outlet Tester with LCD, Complete Set with Carrying Case & Batteries for Electrician, DIY & HVAC
$39.99
View on AmazonDigital Multimeter Voltmeter Battery Voltage Multi Tester Continuity Ohm Volt Amp DC AC Current Resistance Diodes 2000 Counts Electrical Test Meter with Leads Backlight LCD Display
$9.98
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Price as of Jul 24, 2026. Product prices and availability are accurate as of the date indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
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Disclaimer: This calculator provides preliminary estimates for educational purposes only. It is not a substitute for a licensed professional engineer, architect, or structural engineer. Results depend on material grade and species, site conditions, local climate and snow loads, and amendments to the applicable building code, all of which vary by location. Always verify results against your local building codes and confirm requirements with your Authority Having Jurisdiction before proceeding. Do not use these estimates for permitting, fabrication, or construction without stamped, engineer-sealed drawings from a licensed professional. Improperly sized structural members, foundations, or gas lines can cause structural collapse, fire, gas leaks, serious injury, or death.
Example Calculations
2Find resistance: 5V, 20mA LED
Inputs
Voltage5 V
Current0.02 A
Result
Resistance250.000 Ω
Power100.000 mW
R = V / I = 5 / 0.02 = 250Ω. P = 5 × 0.02 = 0.1W = 100mW.
Frequently Asked Questions
QWhat is Ohm's law?
Ohm's law states V = I × R: voltage equals current times resistance. Combined with P = V × I, you can solve for any electrical quantity from two knowns.
- V = I × R (voltage = current × resistance)
- I = V / R (current = voltage / resistance)
- R = V / I (resistance = voltage / current)
- P = V × I = I²R = V²/R (power formulas)
| Known Values | Formula for V | Formula for I | Formula for R | Formula for P |
|---|---|---|---|---|
| V and I | — | — | V/I | V×I |
| V and R | — | V/R | — | V²/R |
| I and R | I×R | — | — | I²×R |
| P and I | P/I | — | P/I² | — |
QHow do I calculate resistance from voltage and current?
Divide voltage by current: R = V / I. For example, 12V across a component drawing 2A means R = 12/2 = 6Ω.
- R = V / I is the most common form
- 12V / 2A = 6 ohms
- If current is in milliamps, convert: 20mA = 0.02A
- Power check: P = 12 × 2 = 24W
QWhat is electrical power and how is it calculated?
Power (watts) = voltage × current. A 12V supply delivering 2A provides 24W. Power also equals I²R or V²/R.
- P = V × I (basic formula)
- P = I² × R (useful when V unknown)
- P = V² / R (useful when I unknown)
- 1 watt = 1 joule per second
QWhen does Ohm's law not apply?
Ohm's law applies to linear (ohmic) devices like resistors. Non-linear components like diodes, transistors, and LEDs don't follow V=IR directly—they have voltage-current curves instead.
- Resistors: always ohmic
- Diodes: non-linear V-I curve
- LEDs: need forward voltage concept
- Capacitors/inductors: impedance varies with frequency
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Last Updated: Jul 24, 2026
This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.