Science & Engineering

Transformer Calculator

Finds an ideal transformer's secondary voltage from the primary voltage and turn counts using Vs = Vp x (Ns / Np), and shows the turns ratio. Enter 120 V, 100 primary turns and 25 secondary turns to get 30 V at a 4:1 ratio.

What this calculator does

The Transformer Calculator estimates your result instantly from the values you enter, using standard science & engineering formulas. Finds an ideal transformer's secondary voltage from the primary voltage and turn counts using Vs = Vp x (Ns / Np), and shows the turns ratio. Enter 120 V, 100 primary turns and 25 secondary turns to get 30 V at a 4:1 ratio. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.

Transformer Calculator

Result

—
Secondary Voltage (V)
—
Turns Ratio

About Transformer Calculator

This tool models an ideal transformer, giving the secondary voltage from the primary voltage and the turn counts with Vs = Vp × Ns / Np. It also reports the turns ratio Np:Ns.

Formula & Mathematical Calculation

Secondary Voltage (V) = f(Primary Voltage (V), Primary Turns, Secondary Turns)

Calculated according to standard science formulas implemented in the calculator core.

Calculation Example

For a primary of 120 V with 100 primary turns and 25 secondary turns: Vs = 120 × 25 / 100. The Secondary Voltage box shows 30 V and the Turns Ratio box shows 4:1, with the note Vs = Vp·(Ns/Np) = 30 V (turns ratio 4:1).

Key Benefits

  • Calculates secondary voltage from primary voltage and turn counts
  • Reports the primary-to-secondary turns ratio
  • Uses the ideal-transformer relation Vs = Vp x Ns/Np
  • Rounds voltage and ratio to three decimal places

How to Use this Calculator

  1. Enter the primary voltage
    Type the primary-side voltage in volts into the Primary Voltage (V) field.
  2. Enter the primary turns
    Type the number of turns on the primary winding into the Primary Turns field.
  3. Enter the secondary turns
    Type the number of turns on the secondary winding into the Secondary Turns field.
  4. Calculate
    Click Calculate and read the Secondary Voltage and Turns Ratio boxes.

Assumptions & Limitations

What the calculation assumes

  • Every value you enter is treated as an exact, known amount.
  • Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
  • Results use standard published formulas and account only for the values entered above.
  • Rounding is applied for display; the underlying calculation uses your full precision.
  • Results are returned in the same units you enter, unless the tool states the output unit.

What it does not cover

  • Transformer Calculator produces a calculated result for reference and learning, not a certified or official measurement.
  • Real-world outcomes differ when tolerances, rounding rules or local standards apply.
  • Definitions and standards vary by region and change over time; verify the convention that applies to your case.
  • Figures are only as accurate as the inputs you supply — check them before acting on the result.
  • For work where the result carries real consequences, confirm it against an authoritative source.

Frequently Asked Questions

It uses the ideal-transformer relation Vs = Vp x Ns / Np.

As Np/Ns to one, for example 4:1 when there are four primary turns per secondary turn.

Primary turns is the divisor in the voltage formula, so a value of zero or less triggers an error.

No. It assumes an ideal transformer, so real-world losses and current are not modelled.

Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.