Documentation sections

Calculator slugs and inputs

All 255 calculators, by category. Send a calculator's slug as slug; its reference lists every input with its unit, range and default, every output, and a real example.

Popular calculator slugs

The most used calculators
Slug	Calculator	Inputs
bldc-winding	BLDC Winding Calculator	targetKv, poleCount, slotCount, statorInnerDia, statorStackLength, maxCurrent, supplyVoltage, windingType
yagi-antenna	Yagi-Uda Antenna Design Calculator	frequency, numElements
filter-designer	LC Filter Calculator — Low-Pass, High-Pass & Band-Pass	responseType, filterType, fc, order, impedance, qFactor, eSeries
coax-loss	Coaxial Cable Loss Calculator	cableIndex, frequencyMHz, lengthM, inputPower
ntc-thermistor	NTC Thermistor Temperature Calculator	resistance, beta, T0, R0, fixedResistor, adcRef, adcBits, ntcPosition
smith-chart	Online Smith Chart Calculator	resistance, reactance, referenceImpedance
pll-loop-filter	PLL Loop Filter Designer	fRef, loopBW, phaseMargin, kvco, n, icp, eSeries
dipole-antenna	Half-Wave Dipole Antenna Calculator	frequency, velocityFactor

Every slug

RF & Microwave Calculators36

PCB Design Calculators36

Signal Processing Calculators14

Antenna Design Calculators11

Communications Calculators11

EMC/EMI Calculators16

Thermal Management Calculators6

Sensor Interface Calculators17

Unit Conversion Calculators19

Audio Electronics Calculators18

IoT & LPWAN Calculators2

The most used: bldc-winding, at its defaults

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "bldc-winding",
    "inputs": {
      "targetKv": 935,
      "poleCount": 14,
      "slotCount": 12,
      "statorInnerDia": 22,
      "statorStackLength": 13,
      "maxCurrent": 5,
      "supplyVoltage": 11.1,
      "windingType": 0
    }
  }'

import rftools

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

result = client.calculate("bldc-winding", {
    "targetKv": 935,
    "poleCount": 14,
    "slotCount": 12,
    "statorInnerDia": 22,
    "statorStackLength": 13,
    "maxCurrent": 5,
    "supplyVoltage": 11.1,
    "windingType": 0,
})
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": "bldc-winding",
    "inputs": {
      "targetKv": 935,
      "poleCount": 14,
      "slotCount": 12,
      "statorInnerDia": 22,
      "statorStackLength": 13,
      "maxCurrent": 5,
      "supplyVoltage": 11.1,
      "windingType": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "bldc-winding",
	  "inputs": {
	    "targetKv": 935,
	    "poleCount": 14,
	    "slotCount": 12,
	    "statorInnerDia": 22,
	    "statorStackLength": 13,
	    "maxCurrent": 5,
	    "supplyVoltage": 11.1,
	    "windingType": 0
	  }
	}`)
	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))
}

200application/json

{
  "slug": "bldc-winding",
  "values": {
    "turnsPerCoil": 4,
    "wireAwg": 18,
    "wireDiameter": 1.024,
    "fillFactor": 47.23709144930302,
    "phaseResistance": 13.876901160598317,
    "coilSpan": 1,
    "windingFactor": 0.9330127018922194,
    "actualKv": 1027.607626225481,
    "deltaEquivKv": 1779.8686188677814,
    "noLoadSpeed": 11406.444651102838
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:bldc-winding",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Hanselman, D. — Brushless Permanent Magnet Motor Design, 2nd ed.; Bianchi, N. & Dai Pré, M., IEE Proc. Electric Power Applications, 2006 (winding factor); Pyrhönen, Jokinen & Hrabovcová, Design of Rotating Electrical Machines, Wiley 2008, section 2.9 (slot fill)",
    "assumptions": [
      {
        "code": "slot-area-inrunner-bore",
        "text": "The slot area is estimated from the stator bore as for an inrunner, 0.55·πd/S wide by 0.2·d deep. An outrunner's slot is smaller, so its real fill factor is higher than shown."
      }
    ],
    "validRange": {
      "status": "inside",
      "bounds": {
        "targetKv": {
          "min": 1,
          "max": 10000,
          "unit": "RPM/V"
        },
        "poleCount": {
          "min": 2,
          "max": 60,
          "unit": "poles"
        },
        "slotCount": {
          "min": 3,
          "max": 72,
          "unit": "slots"
        },
        "statorInnerDia": {
          "min": 5,
          "max": 300,
          "unit": "mm"
        },
        "statorStackLength": {
          "min": 1,
          "max": 200,
          "unit": "mm"
        },
        "maxCurrent": {
          "min": 0.1,
          "max": 500,
          "unit": "A"
        },
        "supplyVoltage": {
          "min": 1,
          "max": 400,
          "unit": "V"
        },
        "windingType": {
          "min": 0,
          "max": 1,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "targetKv": 935,
      "poleCount": 14,
      "slotCount": 12,
      "statorInnerDia": 22,
      "statorStackLength": 13,
      "maxCurrent": 5,
      "supplyVoltage": 11.1,
      "windingType": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}