🔋 Free Tool

Amps to Volts Calculator

Convert current in amps to voltage in volts using power (watts) or resistance (ohms). Supports unit dropdowns (mA–kA, mW–MW, mΩ–MΩ), shows results in mV/V/kV, and provides Ohm's Law reference.

Voltage
120.00 V

How to Convert Amps to Volts

1

Pick Method

Choose "Using Watts" to apply Watt's Law (V = P/I), or "Using Resistance" to apply Ohm's Law (V = I×R).

2

Enter with Units

Input current (mA/A/kA) and either power (mW–MW) or resistance (mΩ–MΩ). Unit conversion is automatic.

3

Read Multi-Unit Result

Voltage shows in V plus mV (for small values) or kV (for large values). Try presets to verify common voltages.

Amps to Volts Formula

Method 1: Using Power (Watt's Law)
V = P ÷ I
V = Voltage (volts), P = Power (watts), I = Current (amps)
Method 2: Using Resistance (Ohm's Law)
V = I × R
V = Voltage (volts), I = Current (amps), R = Resistance (ohms)

The Complete Ohm's Law Wheel (12 Formulas)

From the three fundamental equations (V = IR, P = VI, P = I²R), all twelve circuit formulas can be derived. This "Ohm's Law wheel" lets you solve for any electrical quantity given any two others:

To FindIf You KnowFormula
Voltage (V)I and RV = I × R
P and IV = P / I
P and RV = √(P × R)
Current (I)V and RI = V / R
P and VI = P / V
P and RI = √(P / R)
Resistance (R)V and IR = V / I
V and PR = V² / P
P and IR = P / I²
Power (P)V and IP = V × I
I and RP = I² × R
V and RP = V² / R

Example Calculations

USB Device: 0.5A at 2.5W
V = 2.5 ÷ 0.5 = 5V
Result: 5 Volts
Standard USB 2.0 power. USB 3.0 allows up to 0.9A at 5V (4.5W).
Car Battery: 500A cranking, 6kW
V = 6000 ÷ 500 = 12V
Result: 12 Volts
Cold cranking amps (CCA). Voltage drops to ~10V under cranking load.
Heating Element: 10A through 12Ω
V = 10 × 12 = 120V
Result: 120 Volts
Using Ohm's Law. Power consumed: P = 10² × 12 = 1,200W.
Electric Dryer: 24A at 5760W
V = 5760 ÷ 24 = 240V
Result: 240 Volts
US 240V split-phase circuit. NEMA 14-30 plug with 10 AWG wiring.
LED Strip: 2A through 6Ω
V = 2 × 6 = 12V
Result: 12 Volts
Standard 12V LED strip. Power = 2 × 12 = 24W per meter typical.

Common Voltage Levels Reference

VoltageTypeCommon UseSafety Level
1.5VDCAA/AAA batteriesSafe
3.7VDCLithium-ion cells (phones, laptops)Safe (fire risk if punctured)
5VDCUSB, Arduino, microcontrollersSafe
12VDCAutomotive, LED strips, CCTVSafe
24VDC/ACHVAC control, industrial, doorbellSafe
48VDCTelecom, PoE, golf cartsCaution (borderline)
120VACUS/Canada/Japan household⚠️ Dangerous
230-240VACEU/UK/AU household, US 240V⚠️ Very dangerous
277VACUS commercial lighting⚠️ Very dangerous
480VACUS industrial three-phase☠️ Lethal

⚠️ Voltage Safety Guidelines

  • Generally safe: Below 50V DC or 30V AC RMS in dry conditions. However, wet conditions lower the danger threshold significantly—24V AC can be lethal in a pool or bathtub.
  • Lethal range: 120V AC and above. Human skin resistance varies from 100kΩ (dry) to 1kΩ (wet). At 120V with wet skin: I = 120V / 1000Ω = 120mA—far above the 10mA lethal threshold for cardiac fibrillation.
  • Lock-out/tag-out: Before working on any circuit, disconnect power, lock the breaker, and verify 0V with a multimeter. Test the multimeter on a known live source first to confirm it works.
  • Voltage drop checks: Use V = I × R_wire to verify voltage at the load end. NEC limits: 3% for branch circuits, 5% total. Long runs at high current require thicker wire or higher voltage.

Understanding Amps to Volts Conversion

Converting amps to volts reverses the most fundamental calculation in circuit analysis. While Ohm's Law is usually presented as V = IR (find voltage from current and resistance), in practice, you often know the current draw of a device (from its nameplate or a clamp meter reading) and need to determine what voltage it's operating at—perhaps to verify correct supply voltage or diagnose a problem.

A common practical application is measuring voltage drop across a long wire run. If you know the wire gauge (and thus its resistance per foot) and measure the current with a clamp meter, V = I × R tells you exactly how much voltage is lost in the cable. This is crucial for solar installations, EV charging, and any circuit where the load is far from the panel. A 100-foot run of 12 AWG wire carrying 20A drops about 6.4V—that's 5.3% at 120V, exceeding the NEC 3% recommendation.

For related conversions, use our Volts to Amps Calculator for the reverse direction, our Amps to Watts Calculator to find power from current, or our Watts to Volts Calculator to find voltage from power.

Frequently Asked Questions

You need either watts or resistance. Using watts: V = P ÷ I (Watt's Law rearranged). Using resistance: V = I × R (Ohm's Law). Amps alone cannot be converted to volts without knowing the circuit's power consumption or resistance—they measure different physical quantities (current vs. potential difference).
Two formulas: V = P / I (from Watt's Law P = VI, rearranged). V = I × R (Ohm's Law, the most fundamental equation in circuit analysis, published by Georg Ohm in 1827). Both give voltage in volts. Choose based on whether you know the device's power rating (watts) or the circuit resistance (ohms).
At 100W: V = 100/10 = 10V. At 1,200W: V = 1,200/10 = 120V. At 2,400W: V = 2,400/10 = 240V. Using resistance: with 12Ω: V = 10 × 12 = 120V. With 24Ω: V = 10 × 24 = 240V. The answer always depends on a second known value (power or resistance).
Amps (A) measure current—the rate of electron flow through a conductor (1 amp = 6.24 × 10¹⁸ electrons per second). Volts (V) measure electrical potential difference—the "pressure" driving electrons. Using a water analogy: amps = water flow rate (gallons/minute), volts = water pressure (PSI). Both are needed to determine power (watts = V × A).
Ohm's Law (V = I × R) directly gives voltage from current and resistance. For example, if 5A flows through a 24Ω resistor, the voltage across it is 5 × 24 = 120V. This law applies to all linear (ohmic) conductors at constant temperature. It is the foundation of all circuit analysis and forms the basis for Kirchhoff's Voltage Law.
Voltage drop is the reduction in voltage as current flows through resistance in wiring. V_drop = I × R_wire. NEC recommends max 3% drop for branch circuits and 5% total. Example: 20A through 100ft of 12 AWG wire (3.2 mΩ/ft = 0.32Ω round trip): V_drop = 20 × 0.32 = 6.4V (5.3% at 120V—too high). Use 10 AWG to reduce it.
Use Kirchhoff's Voltage Law (KVL): the sum of all voltages around a closed loop equals zero. For a series circuit with multiple resistors: V_component = I × R_component. The current is the same through all series components, so the voltage divides proportionally to resistance: V₁/V₂ = R₁/R₂ (voltage divider principle).
Standard voltages: 1.5V (AA battery), 3.3V (microcontrollers), 3.7V (lithium-ion cell), 5V (USB), 9V (battery), 12V (automotive), 24V (industrial control, HVAC), 48V (telecom), 120V (US household), 230V (EU household), 240V (US heavy appliances), 277V (US commercial lighting), 480V (US industrial), 600V (Canada industrial).
Voltage determines shock severity: <30V is generally safe for dry skin. 50V AC can be lethal in wet conditions. 120V household current causes severe burns and potential cardiac arrest with 10-20mA passing through the heart. 240V and above is extremely dangerous. Always verify voltage is zero with a multimeter before working on circuits (lock-out/tag-out procedure).
The voltage across an ideal short circuit is 0V (by definition: R = 0, so V = I × 0 = 0V). However, the current becomes extremely high (limited only by the source's internal resistance), which is why short circuits cause sparks, melting, fire, and explosive arc flashes. Circuit breakers and fuses protect against short circuits by interrupting current flow within milliseconds.

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