Transformer turns ratio and voltage calculator
Find what voltage a winding delivers: 230 V on a 1000-turn primary with a 100-turn secondary gives a turns ratio of 10 and an ideal 23 V output, so it is a step-down transformer. Free in your browser.
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Worked example
- Primary voltage
- 230
- Primary turns
- 1,000
- Secondary turns
- 100
- Turns ratio
- 10
- Voltage ratio
- 10
- Secondary voltage
- 23
- Configuration
- step-down
This transformer turns ratio and voltage calculator uses the ideal transformer relationship to find the winding ratio and secondary voltage from three known values: primary voltage, primary turns, and secondary turns. It gives a deterministic result for quick engineering estimates, classroom exercises, design checks, and automated calculations. The response also identifies whether the winding arrangement is step-down, step-up, or unity. Results represent an ideal transformer, so practical losses, winding resistance, regulation, core limits, frequency, and load behavior must be considered separately when designing or evaluating real equipment.
Understand the transformer turns relationship
An ideal transformer links winding voltage directly to winding turns. The governing relationship is Vp divided by Vs equals Np divided by Ns, where Vp is primary voltage, Vs is secondary voltage, Np is primary turns, and Ns is secondary turns. This calculator reports the turns ratio as Np/Ns.
A ratio greater than one means the primary has more turns than the secondary, so the ideal secondary voltage is lower and the arrangement is described as step-down. A ratio below one means the secondary has more turns, producing a step-up arrangement. A ratio of exactly one is a unity transformer: primary and secondary voltages are equal in the ideal model.
The calculation uses voltage magnitudes and does not model phase or polarity marks. Stating that convention matters because some books and instruments display the reciprocal Ns/Np instead. Always inspect the field names before comparing ratios from different sources.
Enter primary voltage and winding turns correctly
Provide the primary voltage in volts and the two physical winding turn counts. Both turn counts must be positive whole numbers because a practical winding contains a countable number of complete turns, and a zero-turn winding would make the transformer relationship undefined. Primary voltage may be zero for a mathematical zero-input case, but it cannot be negative in this magnitude-based calculator.
Use compatible voltage definitions throughout your work. For ordinary sinusoidal power calculations, enter RMS primary voltage and interpret the calculated secondary voltage as RMS. Do not enter a peak primary voltage and then treat the result as RMS without performing the appropriate conversion.
The tool accepts finite numeric values only and rejects missing values, infinity, nonnumeric text, fractional turn counts, zero turns, and negative turns. It calculates Vs as Vp multiplied by Ns and divided by Np. For example, 230 volts applied to a 1,000-turn primary with a 100-turn secondary gives a turns ratio of 10 and an ideal secondary voltage of 23 volts.
No rounding is imposed, preserving the deterministic numeric result for downstream code.
Apply the ideal result safely in real projects
Treat the calculated secondary voltage as a first-order ideal value, not a guarantee for a built transformer under every condition. Real secondary voltage changes with winding resistance, leakage reactance, magnetizing current, core material, operating frequency, temperature, manufacturing tolerances, and load current. A transformer's nameplate secondary voltage is commonly specified at a particular load, while an unloaded measurement can be higher because regulation losses are smaller.
This calculator does not determine current capacity, wire gauge, flux density, core cross-section, insulation class, temperature rise, inrush current, or isolation safety. Those checks remain essential before selecting parts or energizing hardware. The deterministic output is especially useful for comparing candidate winding counts, checking textbook problems, generating expected values in tests, or catching a reversed step-up versus step-down assumption.
In automation, validate that your chosen turns ratio leaves appropriate margin for supply tolerance and load regulation.
What you can do with it
Estimate an ideal secondary voltage
Convert a known primary voltage and two winding turn counts into the ideal secondary voltage before applying real-world regulation margins.
Check transformer coursework
Verify turns-ratio exercises with a clear Np/Ns convention and an explicit step-up, step-down, or unity classification.
FAQ
Which formula does the calculator use?
It uses the ideal transformer relationship Vp/Vs = Np/Ns, rearranged as Vs = Vp × Ns/Np.
Does the result include transformer losses?
No. It is an ideal voltage result and does not model winding resistance, leakage, regulation, core loss, or load current.
Can winding turns be fractional or zero?
No. Primary and secondary turns must both be positive integers; zero would make the relationship undefined.
What does an Np/Ns ratio greater than one mean?
It means the primary has more turns than the secondary, so the ideal transformer is step-down from primary to secondary.
Should I enter RMS or peak voltage?
For ordinary AC power, enter the RMS primary voltage and read the secondary as RMS too. If you start from a peak value, convert it first, or treat the result as a peak value as well.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/eng/transformer-turns \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"primary_voltage":230,"primary_turns":1000,"secondary_turns":100}'const res = await fetch("https://api.kit.forhosting.com/eng/transformer-turns", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"primary_voltage": 230,
"primary_turns": 1000,
"secondary_turns": 100
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/eng/transformer-turns",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"primary_voltage": 230,
"primary_turns": 1000,
"secondary_turns": 100
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/eng/transformer-turns", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"primary_voltage":230,"primary_turns":1000,"secondary_turns":100}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"primary_voltage":230,"primary_turns":1000,"secondary_turns":100}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/eng/transformer-turns", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"primary_voltage": 230,
"primary_turns": 1000,
"secondary_turns": 100
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "eng.transformer_turns",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Understand the transformer turns relationship
Because the same ratio describes both turns and voltage, the tool also reports voltage_ratio using the Np/Ns convention.
Apply the ideal result safely in real projects
API use is charged at the published base price of $0.002 per successful item, while invalid input is returned as a typed error so callers can correct the relevant field.
Integration use cases
Create deterministic engineering test data
Generate repeatable ratio and voltage values for spreadsheets, scripts, design tools, and regression tests without network-dependent computation.
Technical questions
How is the turns ratio defined?
The returned turns_ratio is primary turns divided by secondary turns, or Np/Ns.