RMR calculator
A 30-year-old man weighing 80 kg at 180 cm burns about 1780 kcal a day at rest, by the Mifflin-St Jeor equation. That is your calorie floor before any exercise or digestion is added. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Weight
- 80
- Height
- 180
- Age
- 30
- Sex
- Male
- Rmr kcal day
- 1,780 kcal/day
- Equation
- mifflin_st_jeor
- Weight (kg)
- 80
- Height (cm)
- 180
Resting metabolic rate is the energy a body spends while awake and at rest to keep breathing, circulation, temperature control and cellular repair running. Clinics and consumer apps treat RMR as the practical daily calorie floor, because it is measured under less strict conditions than laboratory basal metabolic rate and is closer to how people actually sit still during a test. The Mifflin-St Jeor equation estimates that floor from four measurements: weight in kilograms, height in centimeters, age in years and biological sex. This capability applies the published coefficients exactly, returns RMR in kilocalories per day, and never mixes in activity, thermic effect of food or wearable guesses. Invalid weight, height or age is rejected instead of inventing a calorie number.
What resting metabolic rate is and how Mifflin-St Jeor estimates it
Resting metabolic rate (RMR) is the number of kilocalories your body burns in twenty-four hours while you are awake, lying still, and not digesting a recent meal. It covers the energy cost of breathing, pumping blood, maintaining ion gradients, and keeping core temperature, and it typically accounts for sixty to seventy-five percent of total daily energy expenditure in a sedentary adult.
Unlike basal metabolic rate, which is measured after an overnight fast in a dark, thermally neutral room with the subject fully at rest, RMR is collected under slightly looser clinical conditions and is the figure most dietitians, coaches and consumer apps actually use as a calorie floor. The Mifflin-St Jeor equation, published in 1990 from indirect calorimetry on contemporary adults, estimates that resting rate from four anthropometric inputs: weight in kilograms, height in centimeters, chronological age in years, and biological sex.
For males the formula is ten times weight plus six point two five times height minus five times age plus five. For females the same weight, height and age terms apply, but the sex constant is minus one hundred sixty-one. Those constants absorb average differences in lean mass observed in the validation cohorts.
The result is a resting energy floor in kilocalories per day, not a total daily energy budget: it does not add exercise, non-exercise activity thermogenesis, the thermic effect of food, fever, pregnancy or illness. Use the number as a baseline, then apply an activity factor or measured intake when you need a full calorie plan.
Where an RMR calculator earns its keep in health and product workflows
Nutrition coaching apps collect onboarding anthropometrics and need a defensible resting calorie number before suggesting macros or a deficit. Clinical research coordinators batch-convert study-subject measurements into RMR for secondary analysis without spreading spreadsheet formulas that diverge by cell. Fitness platforms show members a transparent resting floor next to wearable burn estimates so users understand the difference between sitting still and a training day.
Employer wellness portals can pre-fill educational calculators without shipping a proprietary engine. The browser path is free for single checks: enter eighty kilograms, one hundred eighty centimeters, age thirty, male, and confirm one thousand seven hundred eighty kilocalories per day. Failed validation does not consume balance, so you can probe the contract safely from clients and tests.
What you can do with it
Dietitian calorie floors
Turn clinic weight, height, age and sex into a Mifflin-St Jeor RMR before writing a meal plan or a deficit target.
Fitness app onboarding
Compute a transparent resting kcal/day figure at signup and show it next to activity-adjusted totals in the dashboard.
FAQ
What is RMR and how does this calculator compute it?
Resting metabolic rate is the kilocalories burned in a day at rest.
How is RMR different from BMR?
BMR is measured under stricter laboratory conditions after an overnight fast. RMR is the practical resting figure used in clinics and apps.
Which units should I send?
Weight in kilograms, height in centimeters, age in years. Convert from pounds or inches before calling. Sex must be male or female (m, f, man and woman are also accepted).
Why was my request rejected?
Weight, height and age must each be a positive number (greater than zero). Sex must be male or female (or m/f/man/woman).
How do I get my total daily calories from my RMR?
Multiply your RMR by an activity factor, or compare it with what you actually eat. This calculator deliberately stops at the resting figure, so exercise, everyday movement and the energy used to digest food are not included.
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/health/rmr \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"weight":80,"height":180,"age":30,"sex":"male"}'const res = await fetch("https://api.kit.forhosting.com/health/rmr", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"weight": 80,
"height": 180,
"age": 30,
"sex": "male"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/rmr",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"weight": 80,
"height": 180,
"age": 30,
"sex": "male"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/rmr", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"weight":80,"height":180,"age":30,"sex":"male"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"weight":80,"height":180,"age":30,"sex":"male"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/rmr", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"weight": 80,
"height": 180,
"age": 30,
"sex": "male"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.rmr",
"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
Input contract, response fields, and when the calculator rejects a request
Send four required fields: weight as a positive number in kilograms, height as a positive number in centimeters, age as a positive number of years, and sex as male or female (short forms m, f, man and woman are accepted). Pair this result with your own activity multiplier if you need estimated total daily energy expenditure; this capability deliberately stops at resting metabolic rate so product copy and clinical notes stay honest about what was computed. Aliases such as weight_kg, height_cm, kg, cm, years, age_years and gender map to the same parameters so existing forms can wire in without renaming columns. Weight, height and age must each be a finite number strictly greater than zero; zero, negatives, empty strings, booleans and non-numeric text fail immediately with invalid_input naming the field, and those failures are not billed. Missing or unparseable sex also raises invalid_input. A successful response returns rmr_kcal_day rounded to two decimal places, the normalized sex, the numeric inputs used, the sex_constant applied (plus five or minus one hundred sixty-one), a human-readable formula string that restates Mifflin-St Jeor for that sex, the equation key mifflin_st_jeor, and the unit label kcal/day. There is no network hop, model call or randomness, so the same four numbers always produce the same JSON.
Where an RMR calculator earns its keep in health and product workflows
Developers embed the call in webhooks and batch jobs so every service shares one definition of Mifflin-St Jeor instead of reimplementing float-sensitive multiplies that disagree on rounding. The API path costs $0.002 per successful request and is billed per item, which keeps bulk onboarding scripts cheap while still covering edge execution.
Integration use cases
Research batch pipelines
Convert study-subject anthropometrics into a single audited RMR JSON contract instead of ad-hoc spreadsheet cells.
Technical questions
What does the RMR calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.