Energy converter
One kilowatt-hour is 3,600,000 joules, and one food Calorie is 4184 joules. Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU and electronvolts for lab work, nutrition labels and utility bills. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 1
- Source unit
- kWh
- Target unit
- J
- Result
- 3,600,000
- From label
- kilowatt-hour
- To label
- joule
- Joules
- 3,600,000
An energy converter turns a quantity written in one energy unit into another without hunting conversion tables or rewriting spreadsheet formulas.
Supported units and how the conversion is computed
The converter accepts eight energy families under stable canonical codes: J for joule, kJ for kilojoule, cal for the thermochemical calorie, kcal for the thermochemical kilocalorie (also the nutrition food Calorie written with a capital C), Wh for watt-hour, kWh for kilowatt-hour, BTU for the International Table British thermal unit, and eV for the electronvolt.
Factors follow SI definitions and conventional physics standards: one kilojoule is one thousand joules, one thermochemical calorie is exactly four point one eight four joules, one kilocalorie is four thousand one hundred eighty-four joules, one watt-hour is three thousand six hundred joules, one kilowatt-hour is three million six hundred thousand joules, one International Table BTU is one thousand fifty-five point zero five five eight five two six two joules, and one electronvolt uses the exact CODATA elementary charge times one volt.
Because the intermediate is always joules, converting A to B and B to A is consistent up to the published rounding of twelve decimal places, and there is no pairwise matrix that can drift out of sync. Obsolete mean-calorie or steam-table calorie variants are intentionally out of scope so lab, nutrition, utility, and particle-physics users get predictable results under one clear convention.
Everyday uses: food, utilities and the lab
Use the free in-browser energy converter when you need a quick joules-to-calories, kilowatt-hours-to-BTU, or electronvolts-to-joules check while reading a lab procedure, nutrition label, utility bill, datasheet, or homework problem. Open the page, enter the number and units, and copy the result without installing a spreadsheet, a unit library, or a desktop calculator pack. Source inputs follow the same retention rules as other KIT parse items, and results are safe to cache because the algorithm is fully deterministic.
Authors shipping mobile apps or chatbots can map the result and formula fields directly into cards that show both the number and the conversion path students, dietitians, and engineers expect on paper.
What you can do with it
Nutrition and food labels
Convert kilocalories to kilojoules (and back) so meal logs and recipe databases serve both food Calories and SI energy without hand-written factor tables.
Utilities and building energy
Translate kilowatt-hours, watt-hours, joules, and BTU for audits, smart-meter exports, and HVAC load sheets when suppliers mix SI and customary labels.
FAQ
Which energy units does this converter support?
Joules (J), kilojoules (kJ), thermochemical calories (cal), kilocalories (kcal), watt-hours (Wh), kilowatt-hours (kWh), British thermal units (BTU), and electronvolts (eV).
Is a calorie the food Calorie or the small calorie?
Both use the thermochemical convention, not obsolete steam-table variants.
How do I convert 1 kilowatt-hour to joules?
The response result field is 3600000, plus a joules intermediate and a readable formula.
What happens if I send an unknown unit?
The message names the field and lists supported units. Validation failures are not charged.
Is the energy converter free?
The browser tool runs free on your device.
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/conv/energy \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":1,"from":"J","to":"kWh"}'const res = await fetch("https://api.kit.forhosting.com/conv/energy", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 1,
"from": "J",
"to": "kWh"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/energy",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 1,
"from": "J",
"to": "kWh"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/energy", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":1,"from":"J","to":"kWh"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":1,"from":"J","to":"kWh"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/energy", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"value": 1,
"from": "J",
"to": "kWh"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.energy",
"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 browser tool runs free on your device; the prepaid API charges $0.002 per successful item when pipelines need the same contract from servers and automation.
Supported units and how the conversion is computed
Friendly aliases such as joule, joules, calorie, calories, kilocalorie, watt-hour, kilowatt-hour, btu, electron volt, and electronvolts are normalized case-insensitively so forms and APIs can pass either short codes or full names. Every request multiplies the input value by the exact joules-per-unit factor for the source, then divides by the joules-per-unit factor for the target.
Request shape, response fields, and unknown-unit errors
The error message names the bad field and lists the supported set so clients can correct forms without guessing. Negative values are allowed when you need signed energy deltas in engineering pipelines; zero converts cleanly to zero in every target unit. Send a JSON body with three required fields: value as a finite number, from as the source unit string, and to as the target unit string. Aliases amount and quantity are accepted for value; unit_from and source for from; unit_to and target for to. On success the response echoes the canonical from and to codes, human-readable from_label and to_label strings, the converted result, the intermediate joules quantity, the dimensionless factor from source to target, a short formula line suitable for UI display, the method tag energy_si_codata, and the fixed list of units_supported. Missing value, non-finite numbers such as NaN or Infinity, missing unit fields, and any token that does not map to a supported unit fail with invalid_input and are not charged after the engine rejects the request. Identical inputs always yield identical JSON because the path is pure arithmetic with no randomness, no remote lookup, and no dependence on the wall clock, which makes the endpoint safe to pin in continuous-integration goldens and SDK contract tests. Electronvolt-scale results and kilowatt-hour-scale results share the same code path, so extreme magnitude pairs remain well-defined as long as IEEE double precision can represent the intermediate joules product.
Browser use, API pricing, and everyday workflows
Switch to the prepaid API when an energy-audit app, building-management system, meal-tracking platform, laboratory LIMS, physics homework checker, or smart-meter pipeline must convert energy at scale under a stable KIT contract at $0.002 per successful item; validation failures that raise invalid_input do not consume balance after rejection. Pair this endpoint with power or temperature converters when a product pipeline needs several measure families, or call it alone when search traffic is specifically for energy conversion—joules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, and electronvolts—rather than a general unit switchboard.
Integration use cases
Lab and particle-physics pipelines
Normalize eV, joules, and calories in LIMS and homework checkers with a prepaid, deterministic API contract and clear invalid_input on unknown units.