Cold-start warm-up fuel calculator
Five minutes of cold-start idling at 1.2 litres per hour burns 0.1 litre of fuel: the warm-up burn rate multiplied by the idling time in hours, in litres, gallons or any volume unit you choose. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Warmup minutes
- 5
- Idle burn rate
- 1.2
- Fuel price
- 1.65
- Warmup hours
- 0.0833333333
- Extra fuel
- 0.1
- Extra cost
- 0.165
Cold engines burn more fuel while idling to warm up than the same vehicle does at a stable hot idle. Drivers, fleet managers, and eco-driving coaches often ask how much gas or diesel that morning warm-up really costs—especially in winter when five or ten minutes at elevated idle is common.
How cold-start warm-up fuel is estimated from duration and idle burn rate
During a cold start, many drivers leave the engine idling until cabin heat, defrost, or oil temperature feels ready. That idle is not free: injectors or carburetors deliver a richer mixture and friction is higher until the powertrain reaches operating temperature, so the fuel burned per minute is often higher than a fully warm idle. This capability models that window with one transparent product: extra fuel equals the elevated idle burn rate times warm-up duration expressed in hours.
If you measure or look up an idle burn of one point two litres per hour and you idle for five minutes, the duration in hours is five divided by sixty, which is one twelfth of an hour, and extra fuel is one point two times one twelfth, or zero point one litre. The same identity works with US gallons per hour or any other volume unit you choose, as long as the burn rate and any optional fuel price share that volume unit.
The calculator does not invent a default burn rate from vehicle year or ambient temperature; you supply the elevated rate that matches your car, truck, or published idle data. Non-positive minutes or rates are rejected so a zero or inverted sensor reading cannot produce a nonsense negative tank credit or a divide-by-zero style edge case.
What you can do with it
Winter morning warm-up budgets
Drivers enter idle minutes and an elevated L/h or gal/h rate to see how much fuel (and optional money) a cold-start defrost or cabin warm-up actually uses.
FAQ
Is the cold-start warm-up fuel calculator free?
The browser tool runs free on your device.
Does it use weather, vehicle year, or live gas prices?
No. You supply the elevated idle rate and duration (and optional price). Ambient models, OBD lookups, and live pumps are outside this pure rate-times-time estimate.
Why does a cold engine burn more fuel at idle?
Until it reaches operating temperature, the engine runs a richer fuel mixture and has more friction. So it burns more fuel per minute than at a fully warm idle, which is why the rate you enter should be the elevated warm-up one.
Does the result subtract the fuel a warm engine would use anyway?
No. The result is all the fuel burned at the rate you enter during the warm-up. If you only want the extra over a warm idle, subtract the warm idle rate from your warm-up rate before entering it.
Can I use gallons per hour instead of litres?
Yes. The formula works with US gallons per hour or any other volume unit, and the result comes out in that same unit. If you add a fuel price, it must be for that unit too, never a gallon rate with a price per litre.
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/travel/cold-start-fuel \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"warmup_minutes":5,"idle_burn_rate":1.2}'const res = await fetch("https://api.kit.forhosting.com/travel/cold-start-fuel", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"warmup_minutes": 5,
"idle_burn_rate": 1.2
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/travel/cold-start-fuel",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"warmup_minutes": 5,
"idle_burn_rate": 1.2
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/travel/cold-start-fuel", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"warmup_minutes":5,"idle_burn_rate":1.2}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"warmup_minutes":5,"idle_burn_rate":1.2}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/travel/cold-start-fuel", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"warmup_minutes": 5,
"idle_burn_rate": 1.2
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "travel.cold_start_fuel",
"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
This cold-start warm-up fuel calculator multiplies your elevated idle burn rate (volume per hour) by warm-up duration in hours derived from minutes, returning extra_fuel in the same volume unit and, when you supply a pump price, extra_cost in currency. The pure arithmetic is free in the browser and costs $0.002 per successful API item, with identical deterministic results on both paths so trip budgets, fleet dashboards, and classroom demos never disagree on a simple rate-times-time estimate.
How cold-start warm-up fuel is estimated from duration and idle burn rate
It also does not subtract a hot-idle baseline unless you do that yourself before sending idle_burn_rate—the field is the rate you treat as the warm-up idle burn, so the product is the fuel volume attributed to that idling window. Results are pure floating-point with stable rounding: identical inputs always yield identical JSON, with no network lookup, random seed, or wall clock involved.
Input contract, response fields, units, and error behaviour
Both must be strictly greater than zero. Example: five minutes at one point two litres per hour yields zero point one litre of extra fuel; at one point sixty-five currency units per litre the extra cost is zero point one six five. Keep units coherent yourself—do not mix gallons-per-hour rates with a price per litre without converting first. POST a JSON body with two required finite numbers: warmup_minutes, the cold-start warm-up idling duration in minutes, and idle_burn_rate, the elevated idle fuel-burn rate in volume units per hour. Aliases for duration include minutes, warmup, warm_up_minutes, idle_minutes, duration_minutes, and duration. Aliases for rate include burn_rate, idle_rate, fuel_rate, rate, liters_per_hour, and gal_per_hour. Optionally send fuel_price (aliases price, price_per_unit, gas_price, fuel_unit_price) as a non-negative price per the same volume unit used in the burn rate; when present the response adds extra_cost equal to extra_fuel times fuel_price. Numeric fields may arrive as JSON numbers or numeric strings. Missing fields, empty strings, NaN, Infinity, non-positive duration or rate, and negative price all fail with invalid_input and are not billed. On success the body echoes cleaned warmup_minutes and idle_burn_rate, warmup_hours as minutes divided by sixty, extra_fuel as rate times hours, a human-readable formula string, and method cold_start_warmup_fuel. When fuel_price was supplied it is echoed and extra_cost is included; optional fields are omitted entirely when unused rather than set to null. Magnitude caps keep results finite on the Worker isolate. Pair the volume with your own seasonal notes or OEM idle specs; this endpoint only multiplies rate by time and does not model coolant maps, accessory load, or ambient temperature curves.
API usage, pricing, travel workflows, and practical limits
Call the free in-browser cold-start warm-up fuel calculator for personal winter planning, driver-education demos, and quick comparisons of short versus long idle habits without installing a spreadsheet. Typical workflows include converting OBD or manufacturer idle-flow figures into a per-start fuel line, summing several cold starts in a multi-leg day client-side, or teaching that a long warm-up burns measurable volume even before the first mile. Use the prepaid API when a fleet portal, expense tool, travel app, or eco-coaching product needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance. Authors shipping SDKs can map extra_fuel and optional extra_cost into tables next to trip fuel cost or trip fuel volume endpoints—this capability answers only the idling warm-up slice, not highway distance economy. It does not look up live fuel prices, weather, or vehicle databases; combine it with a price converter or your own telematics feed when you need those. Keep requests small, document the volume unit you chose for idle_burn_rate, and you get reproducible cold-start fuel estimates for dashboards, LMS modules, and edge workers without hosting custom arithmetic of your own.
Integration use cases
Fleet idle and cold-start reporting
Fleet tools convert telematics warm-up durations and vehicle idle burn rates into deterministic extra_fuel lines for cost and emissions coaching.
Eco-driving education and demos
Instructors and content sites show students that long warm-up idling multiplies rate by time, using the free browser widget that matches the API.
Technical questions
How do I estimate cold-start warm-up fuel with this calculator?
Send warmup_minutes and idle_burn_rate (volume per hour during elevated idle). The response includes extra_fuel = rate × (minutes / 60). Optionally add fuel_price for extra_cost.
What units should I use for idle_burn_rate?
Any volume per hour that matches how you measure fuel—litres per hour, US gallons per hour, and similar. Keep fuel_price in the same volume unit if you request a cost.
What happens if warm-up minutes or burn rate is zero or negative?
The request fails with invalid_input. Non-positive duration or idle_burn_rate is rejected so the engine never returns a nonsense fuel volume.