Output power from efficiency calculator
Find what a motor, drive or converter really delivers: 750 W in at 84 % efficiency gives 630 W of useful output, with the other 120 W lost. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Input power watts
- 750
- Efficiency percent
- 84
- Output power watts
- 630
This output power from efficiency calculator converts a rated or measured input power into the useful power delivered by a machine, motor, drive, converter, or other energy system. Enter input power in watts and efficiency as a percentage, and it applies the standard relationship between input, efficiency, and output. The result is returned in watts with the normalized inputs and formula, making it easy to inspect manually or use in an automated workflow. Efficiency may be anywhere from zero through one hundred percent; values outside that physical percentage range are rejected instead of producing a misleading answer.
How output power is calculated from efficiency
Efficiency describes the fraction of supplied power that becomes useful output. A percentage must first be understood as a ratio: 84 percent means 0.84 of the input reaches the useful output. If a device receives 750 watts at 84 percent efficiency, it delivers 630 watts of useful output, while the remaining 120 watts represents losses under the assumptions of the stated efficiency.
The calculation works at the two physical boundaries as well. Zero percent produces zero useful output, and one hundred percent makes output equal input. Input power must also be finite and non-negative.
This keeps the result aligned with the calculator's purpose: computing a non-negative useful power magnitude from a non-negative supplied power. The relationship is deterministic and contains no hidden equipment model, lookup table, network request, current date, or random value.
Choose input values and interpret the watts result
Use the actual input power that corresponds to the efficiency figure you have. For a motor, that might be electrical power drawn at a documented operating point; for a gearbox, it might be mechanical shaft power entering the transmission; for a converter, it may be measured electrical power at its input terminals. Enter that quantity in watts, then enter efficiency in percent rather than as a decimal fraction.
For example, submit 92 for ninety-two percent, not 0.92. Keep the system boundary consistent: an efficiency measured for one stage should not be applied as though it represented an entire chain. If several stages have separate efficiencies, calculate each stage in sequence or multiply their decimal efficiency ratios before applying the combined value.
The calculator does not infer uncertainty, load variation, duty cycle, or measurement error. Its output is only as representative as the input power and efficiency selected for the same operating condition.
Validate engineering estimates without hiding bad percentages
The most useful role of a small calculator like this is to make assumptions explicit and repeatable. Equipment selection sheets can turn a known input rating and expected efficiency into a quick useful-power estimate. Laboratory scripts can compare measured output with the value predicted from a manufacturer's efficiency point.
Maintenance teams can check whether a proposed replacement has enough delivered power after expected conversion losses. Educational exercises can demonstrate why a system with less than one hundred percent efficiency must return less useful output power than it receives. Strict validation matters in all of these settings.
A negative efficiency or a value above one hundred usually indicates a unit mistake, an incorrectly scaled ratio, or a field mapped from the wrong source. Returning an error makes that defect visible before it spreads into sizing, energy, or cost calculations. The same applies to missing, non-numeric, infinite, or negative input power.
The calculator reports output in watts and does not automatically convert kilowatts, horsepower, energy, torque, or heat. Convert the input to watts first, and use a separate converter or engineering model when the requested quantity is not power.
What you can do with it
Estimate motor shaft output
Apply a motor efficiency percentage to its electrical input power to estimate useful mechanical output in watts.
Check converter delivery
Calculate the useful output available from a power converter at a specified input and operating-point efficiency.
FAQ
Should I enter efficiency as 85 or 0.85?
Enter 85 for an efficiency of eighty-five percent. The field expects a percentage from 0 through 100, not a decimal ratio.
Can input power be zero?
Yes. Zero input power is valid and produces zero output power at every accepted efficiency percentage.
How is output power calculated from efficiency?
Multiply the input power by the efficiency percentage and divide by 100. A device that receives 750 watts at 84 percent efficiency delivers 630 watts of useful output.
How much power is lost?
The difference between input and output. In the example of 750 watts at 84 percent, 120 watts are lost under the assumptions of the stated efficiency.
Can efficiency be above 100 percent?
No. Values from zero through one hundred percent are accepted, and anything outside that range is rejected instead of giving a misleading answer. At zero percent the output is zero; at one hundred it equals the input.
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/mech/output-power-efficiency \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"input_power_watts":750,"efficiency_percent":84}'const res = await fetch("https://api.kit.forhosting.com/mech/output-power-efficiency", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"input_power_watts": 750,
"efficiency_percent": 84
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/mech/output-power-efficiency",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"input_power_watts": 750,
"efficiency_percent": 84
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/mech/output-power-efficiency", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"input_power_watts":750,"efficiency_percent":84}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"input_power_watts":750,"efficiency_percent":84}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/mech/output-power-efficiency", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"input_power_watts": 750,
"efficiency_percent": 84
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "mech.output_power_efficiency",
"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
How output power is calculated from efficiency
The calculator therefore uses P_out = P_in × efficiency_percent / 100. Those endpoints are accepted deliberately, while any percentage below zero or above one hundred triggers an invalid-input error. Identical numeric inputs always return the same JSON result.
Choose input values and interpret the watts result
The response repeats the cleaned input power and efficiency, returns output_power_watts, and includes the formula string so downstream software can display the method without guessing. API requests use the published base price of $0.002 per item.
Integration use cases
Build repeatable engineering worksheets
Use the deterministic API result in equipment comparisons, classroom examples, and automated validation pipelines.
Technical questions
What formula does the calculator use?
It uses P_out = P_in × efficiency_percent / 100 and returns the useful output power in watts.
What happens if efficiency is above 100 percent or below zero?
The request fails with invalid_input because efficiency must remain within the inclusive range from 0 to 100 percent.
How much does the API request cost?
Each successful API request uses the published base price of $0.002. The browser calculator is free to run locally.