Documentation sections

Audio Power Amplifier Calculator

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

Slug audio-power-amplifier. Calculate amplifier output power from supply voltage and speaker impedance. Get max power, RMS power, THD estimate by class (A/AB/D), SNR, and input sensitivity for speaker matching.

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 audio-power-amplifier
Name	Unit	Range	Default	Description
vccnumber	V	1 … 100	12	Single supply voltage powering the amplifier
rlnumber	Ω	1 … 1000	8	Speaker load impedance (common: 4Ω, 8Ω, 16Ω)
efficiencynumber	%	1 … 99	70	Amplifier efficiency: Class A ≈ 20%, Class AB ≈ 70%, Class D ≈ 90%
gainnumber	dB	0 … 80	26	Amplifier voltage gain

Outputs

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

Outputs of audio-power-amplifier
Field	Unit	Description
poutMaxheadline	W	Maximum output power at clipping (Vout_peak² / 2RL)
poutRMS	W	Typical RMS power for program material (≈50% of max)
thd_level	%	Typical total harmonic distortion estimate by amplifier class
snr	dB	Approximate signal-to-noise ratio estimate
inputSensitivity	mV	RMS input voltage required for full output power

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": "audio-power-amplifier",
    "inputs": {
      "vcc": 12,
      "rl": 8,
      "efficiency": 70,
      "gain": 26
    }
  }'

import rftools

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

result = client.calculate("audio-power-amplifier", {"vcc": 12, "rl": 8, "efficiency": 70, "gain": 26})
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": "audio-power-amplifier",
    "inputs": {
      "vcc": 12,
      "rl": 8,
      "efficiency": 70,
      "gain": 26
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "audio-power-amplifier",
	  "inputs": {
	    "vcc": 12,
	    "rl": 8,
	    "efficiency": 70,
	    "gain": 26
	  }
	}`)
	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": "audio-power-amplifier",
  "values": {
    "poutMax": 1.8225000000000002,
    "poutRMS": 0.9112500000000001,
    "thd_level": 0.1,
    "snr": 109,
    "inputSensitivity": 191.37216143266417
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:audio-power-amplifier",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Cordell, \"Designing Audio Power Amplifiers\" 2nd ed.",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "vcc": {
          "min": 1,
          "max": 100,
          "unit": "V"
        },
        "rl": {
          "min": 1,
          "max": 1000,
          "unit": "Ω"
        },
        "efficiency": {
          "min": 1,
          "max": 99,
          "unit": "%"
        },
        "gain": {
          "min": 0,
          "max": 80,
          "unit": "dB"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "vcc": 12,
      "rl": 8,
      "efficiency": 70,
      "gain": 26
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "vcc"
      ],
      "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 pageAudio Power Amplifier Calculator, at these values