Voltage from power and current calculator
A heater drawing 1500 W at 12.5 A runs on 120 V: enter the watts and amps you measured and get the voltage, worked out as power divided by current. Meant for DC and resistive loads. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Power watts
- 1,500
- Current amperes
- 12.5
- Voltage volts
- 120
This voltage from power and current calculator finds electrical voltage when wattage and amperage are the two measurements you already have. Enter real power in watts and current in amperes, and the calculator applies V equals P divided by I to return volts. It is useful for checking device labels, bench measurements, battery-powered equipment, heaters, and other straightforward electrical loads.
When power and current are enough to calculate voltage
Electrical power, voltage, and current are connected by the familiar relationship P equals V times I. Rearranging that identity gives V equals P divided by I, so measured watts and amperes are enough to recover volts. Common examples include resistive heaters, incandescent lamps, simple DC motors under a measured operating condition, battery loads, and electronics tested with a power analyzer.
Keep all inputs in base SI units: watts for power and amperes for current. If a label gives kilowatts, multiply by one thousand first; if a meter gives milliamperes, divide by one thousand. Consistent units are essential because the calculator does not guess prefixes or silently convert them.
Signed values are retained, allowing engineering workflows that use negative power or current to represent direction, but the sign must be interpreted according to the reference convention used by the measurement system.
Interpreting the result for real electrical equipment
Treat the calculated voltage as accurate only to the quality and meaning of the measurements supplied. A device nameplate may state maximum, nominal, or rounded power rather than power at the exact measured current, so dividing two label values can produce an estimate rather than a live terminal voltage. Alternating-current equipment introduces another important limitation: for motors, switch-mode supplies, transformers, and other reactive or nonlinear loads, real power is not generally equal to RMS voltage multiplied by RMS current.
Power factor is also involved, and this simple two-input calculation cannot infer it. Use a dedicated AC or three-phase calculator when phase angle, apparent power, line configuration, or power factor matters. For a resistive load or a DC operating point, the result is often a useful cross-check against a voltmeter, specification sheet, or data acquisition channel.
It can also reveal a unit-entry mistake: an unexpectedly enormous answer may mean milliamperes were entered as amperes or kilowatts as watts. The browser tool is convenient for individual checks.
What you can do with it
Check a device operating point
Convert a measured wattage and current draw into an estimated terminal voltage for a DC or resistive load.
Validate laboratory measurements
Compare voltage derived from a power analyzer and ammeter with the voltage reported by another instrument.
Automate equipment data processing
Derive a consistent voltage field from stored power and current readings in test, inventory, or monitoring pipelines.
FAQ
What formula does the calculator use?
It uses V = P / I: voltage in volts equals real power in watts divided by current in amperes.
Does this calculation work for AC equipment?
It works directly for pure resistive AC loads using compatible RMS measurements. Reactive, nonlinear, and three-phase loads may require power factor and phase information.
Which units should I enter?
Enter power in watts and current in amperes.
Why does the calculator refuse a current of zero?
Because voltage is power divided by current, and dividing by zero has no finite answer. Instead of showing infinity or a made-up figure, the calculator asks you for a real, non-zero current.
Is the result the same as what a voltmeter would show?
Only if both readings were taken at the same moment. A nameplate often lists maximum, nominal or rounded power, so dividing two label figures gives an estimate, not the live voltage at the terminals.
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/elec/voltage-from-power-current \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"power_watts":1500,"current_amperes":12.5}'const res = await fetch("https://api.kit.forhosting.com/elec/voltage-from-power-current", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"power_watts": 1500,
"current_amperes": 12.5
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/voltage-from-power-current",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"power_watts": 1500,
"current_amperes": 12.5
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/voltage-from-power-current", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"power_watts":1500,"current_amperes":12.5}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"power_watts":1500,"current_amperes":12.5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/voltage-from-power-current", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"power_watts": 1500,
"current_amperes": 12.5
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.voltage_from_power_current",
"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
The calculation is deterministic, rejects zero current instead of returning infinity, and uses the same pure arithmetic in the browser and API. Browser calculations are free, while automated API requests cost $0.002 per successful item.
When power and current are enough to calculate voltage
Enter the real power as power_watts and the measured current as current_amperes. The result reports voltage_volts and echoes both inputs alongside the formula, making it easy to display, log, or verify the calculation. This direct relationship is appropriate for direct-current circuits and pure resistive alternating-current loads when the current and voltage measurements use compatible RMS values.
How the division is validated and reported
Current cannot equal zero because division by zero does not define a finite voltage. Extremely large magnitudes are also rejected before arithmetic so output remains stable and serializable. The algorithm validates that the request is an object and that both required quantities are finite numbers. Numeric strings are accepted for practical form and API use, and the documented aliases power, watts, or P can identify power while current, amps, amperes, or I can identify current. Instead of emitting Infinity or a misleading placeholder, the capability returns an invalid_input error whose message explains the zero-current problem. For a valid request, voltage is calculated once as power_watts divided by current_amperes and normalized to fifteen significant digits to reduce insignificant binary floating-point noise while preserving useful engineering precision. No external service, random value, stored state, or current time participates in the result, so identical requests always produce identical JSON. The response includes voltage_volts, power_watts, current_amperes, and the formula V = P / I. That explicit shape lets a user interface show both the answer and its provenance, while an automated system can retain the source readings with the derived voltage for later inspection or testing.
Interpreting the result for real electrical equipment
For test benches, inventory systems, support tools, and engineering pipelines, the API provides the identical deterministic contract at $0.002 per successful item, allowing the calculation to be reproduced consistently across many measured devices.
Technical questions
Can current be zero?
No. Zero current would require division by zero, so the capability returns invalid_input rather than an infinite or undefined voltage.
How much does the calculator cost?
It is free in the browser. Each successful API item costs $0.002; invalid input is rejected with a clear error.