Documentation sections

Transformer Turns Ratio Calculator

POSThttps://rftools.io/api/py/v1/calculate

Slug transformer-turns-ratio. Calculate transformer turns ratio, secondary current, apparent power, and real power delivered. Accounts for transformer efficiency.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of transformer-turns-ratio
Name	Unit	Range	Default	Description
vPrimarynumber	V	0.1 … 100000	120	Primary (input) winding voltage
vSecondarynumber	V	0.1 … 100000	12	Secondary (output) winding voltage
iPrimarynumber	A	0.0001 … 10000	0.1	Primary winding current
efficiencynumber	%	1 … 100	95	Transformer efficiency (typical: 90-99% for power transformers)

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of transformer-turns-ratio
Field	Unit	Description
turnsRatioheadline	none	Transformer turns ratio Np/Ns = Vp/Vs
iSecondary	A	Secondary winding current accounting for efficiency
apparentPower	VA	Apparent power on primary side: Vp × Ip
realPower	W	Real power delivered to secondary: VA × efficiency
couplingFactor	none	Magnetic coupling factor (approximated from efficiency)

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "transformer-turns-ratio",
    "inputs": {
      "vPrimary": 120,
      "vSecondary": 12,
      "iPrimary": 0.1,
      "efficiency": 95
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("transformer-turns-ratio", {"vPrimary": 120, "vSecondary": 12, "iPrimary": 0.1, "efficiency": 95})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "transformer-turns-ratio",
    "inputs": {
      "vPrimary": 120,
      "vSecondary": 12,
      "iPrimary": 0.1,
      "efficiency": 95
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "transformer-turns-ratio",
	  "inputs": {
	    "vPrimary": 120,
	    "vSecondary": 12,
	    "iPrimary": 0.1,
	    "efficiency": 95
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "transformer-turns-ratio",
  "values": {
    "turnsRatio": 10,
    "iSecondary": 0.95,
    "apparentPower": 12,
    "realPower": 11.399999999999999,
    "couplingFactor": 0.95
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:transformer-turns-ratio",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Faraday's Law of Electromagnetic Induction",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "vPrimary": {
          "min": 0.1,
          "max": 100000,
          "unit": "V"
        },
        "vSecondary": {
          "min": 0.1,
          "max": 100000,
          "unit": "V"
        },
        "iPrimary": {
          "min": 0.0001,
          "max": 10000,
          "unit": "A"
        },
        "efficiency": {
          "min": 1,
          "max": 100,
          "unit": "%"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "vPrimary": 120,
      "vSecondary": 12,
      "iPrimary": 0.1,
      "efficiency": 95
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "vPrimary"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageTransformer Turns Ratio Calculator, at these values