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Rojony Khatun Author
Rojony Khatun
CalculatorToolsProjectExpert
Reviewers
Małgorzata Koperska, MD Steven Wooding
Last updated: October 1, 2025

Terminal Voltage Calculator | Formula, EMF & Examples

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Terminal Voltage Calculator

Calculate the terminal voltage of a battery or generator using EMF, internal resistance, and load current with this simple tool and formula.

internal resistance voltage calculator

The real voltage on the terminals of a battery or generator is referred to as terminal voltage. Formula: Vt = E - I × r.

Formula & Table Summary:

FormulaDescription
Vt = E - I × rTerminal voltage formula
Vt = ENo load condition
Vt < EUnder load condition

emf and terminal voltage formula

Terminal Voltage Calculator assists in determining the actual output voltage of a battery or generator with reference to EMF, load-current, and internal resistance.

generator terminal voltage

EMF (E) (V)Internal Resistance (Ω)Current (A)Terminal Voltage (V)
120.2511
240.11023
480.52038
60.0525.9

Frequently Asked Questions - Terminal Voltage Calculator:

What is terminal voltage?

Terminal voltage is the actual voltage available at the terminals of a source when current flows through it.

How do you calculate terminal voltage?

Use Vt = E - I × r, where E is EMF, I is current, and r is internal resistance.

What is the difference between EMF and terminal voltage?

EMF is the ideal source voltage, while terminal voltage is the practical output under load.

When is terminal voltage equal to EMF?

When no current flows (open circuit), terminal voltage equals EMF.

Why is terminal voltage less than EMF under load?

Because of the voltage drop across the source's internal resistance.

Can terminal voltage be higher than EMF?

Yes, in charging conditions, terminal voltage can exceed EMF.

What units are used?

Voltage is measured in volts (V), current in amperes (A), resistance in ohms (Ω).

Is internal resistance important?

Yes, it affects battery efficiency and output voltage under load.

Can this calculator be used for generators?

Yes, it works for both batteries and generators.

Why does battery voltage drop under load?

Because internal resistance consumes part of the EMF, reducing the output.

Rojony Khatun

Rojony Khatun

CalculatorToolsProject

Rojony Khatun is the creator of a free online tools website designed to simplify everyday and engineering-related calculations for students, professionals, and hobbyists. The platform offers a wide variety of basic and advanced calculators across key categories, including Electrical Calculators, Electronic Calculators, and Time & Date Calculators, helping users solve problems quickly and accurately.