You burn roughly your body weight in kilograms per hour of sleep; an 8-hour night equals about 8× that number.
Lower Range
Typical Range
Upper Range
Basic
- Use 1.0 MET for sleep
- Weight in kg × hours
- Fast ballpark
Quick math
Better
- Estimate BMR first
- BMR × hours/24
- Add room temp note
Balanced view
Best
- Track room temp
- Stable schedule
- Lean mass trend
More context
What The Overnight Number Really Means
Sleep counts as a low-effort activity. In the standard activity tables, sleeping carries an intensity of 1.0 MET, which matches quiet rest. MET is a simple scale where “1” equals resting energy use and higher numbers mark harder work. With that in hand, you can turn hours in bed into an energy estimate that lines up with your body size.
The quick rule is tidy: calories per hour ≈ body weight in kilograms when sleep MET is 1.0. A 68-kg adult lands near 68 calories per hour, so an 8-hour stretch is close to 544 calories. It won’t be exact to the single digit, yet it’s consistent and easy to repeat.
Overnight Calorie Burn Calculator: Step-By-Step
Use the widget below for two estimates. The first (MET method) multiplies your weight by your hours in bed. The second (BMR share) starts with an estimated basal day and takes the fraction that matches your time asleep.
const metSleep = 1.0 * tempAdj(t); // base 1.0 MET with a gentle temp nudge const kcalMet = wt * metSleep * hrs; // 1 MET ≈ 1 kcal/kg/hour
const bmr = mifflin(sex, wt, ht, age); // kcal/day const kcalBmrShare = bmr * (hrs/24) * tempAdj(t);
const out = document.querySelector('#out div'); out.innerHTML = `
Math: 1.0 MET × ${wt} kg × ${hrs} h${t!=='neutral' ? ` × temp factor` : ``}
Math: BMR ${bmr.toFixed(0)} × ${hrs}/24${t!=='neutral' ? ` × temp factor` : ``}
`; } calcSleep();
Sleep Calories By Body Size
Here’s a broad table using the 1.0-MET convention. Pick the line closest to your weight. Multiply the per-hour line by your time in bed for a quick estimate.
| Body Weight (kg) | Calories Per Hour | Calories In 8 Hours |
|---|---|---|
| 50 | ~50 | ~400 |
| 60 | ~60 | ~480 |
| 70 | ~70 | ~560 |
| 80 | ~80 | ~640 |
| 90 | ~90 | ~720 |
| 100 | ~100 | ~800 |
The rows above come from a simple truth: 1 MET ≈ 1 kilocalorie per kilogram per hour. Sleep sits near that baseline. If you prefer a daily frame, the BMR share method gives a similar picture once you plug hours into the fraction of a day.
Snacks, late-night meals, or a warm bedroom can nudge these numbers. Cool rooms may lift the estimate a touch because the body defends temperature. Warm spaces may shave a tiny amount. For deeper planning, set your daily calorie needs first so your night math matches your day goals.
Why METs Make The Math Easy
MET stands for metabolic equivalent of task. It’s a standard way to label intensity so you can compare activities. Sitting quietly sits near 1–1.5 METs. Jogging jumps to higher numbers. Sleep stays at 1.0, which keeps the calculator simple. Harvard’s overview of METs explains the scale and how intensity tiers map to daily movement patterns, a handy reference for anyone pairing step goals with rest.
Two Ways To Estimate Night Calories
Method A: MET × Weight × Hours. Use 1.0 for the sleep MET. Multiply by your weight in kilograms and the hours in bed. This mirrors the standard activity approach and lines up with the 1-kcal/kg/hour convention for resting-level tasks.
Method B: BMR × Hours/24. Start with an estimated basal day using a common predictive equation. Take the share that matches your time asleep. If you sleep 8 hours, that’s one-third of a basal day. The calculator above does this for you using the Mifflin-St Jeor equation.
Inputs That Shift Your Result
Body Size. Bigger bodies burn more per hour, so the MET method scales in a straight line with weight.
Room Temperature. A cooler bedroom can raise the estimate slightly as your body works to stay warm. A warmer bedroom can do the reverse. The widget includes a small temperature tag to reflect this.
Sleep Time And Regularity. Short nights leave less total burn, plain and simple. A steady schedule helps your nightly share look the same from day to day.
Lean Mass. More muscle usually means a higher basal day. That shows up in the BMR share method.
Trusted Numbers Behind The Calculator
The sleep MET of 1.0 comes from the latest activity compendium used by exercise scientists and clinicians. It’s a clean way to translate hours in bed to energy. For a deeper primer on the MET scale and intensity buckets, Harvard’s short explainer is a friendly read for non-specialists.
To turn METs into calories for any activity, universities often teach the same simple conversion used in this page’s math. That step bridges a reference table and your personal numbers without special devices or lab gear.
External References Used In This Guide
Accuracy, Limits, And A Smarter Way To Use The Number
These estimates are steady enough for planning. They aren’t a medical measurement. A lab test with indirect calorimetry would pin your exact basal day, but most of us don’t need that for daily choices. What matters is using the same method over time so your comparisons stay clean.
If your goal is fat loss, the night number is just one piece of the day. A realistic calorie target and some movement you enjoy will drive most of the change. Think of the overnight result as a baseline that keeps going whether you’re training or taking a rest day.
When To Favor Each Method
| Method | Formula | Best Use |
|---|---|---|
| MET Method | 1.0 × kg × hours | Fast estimate; trend tracking |
| BMR Share | BMR × hours/24 | When you already manage intake by BMR/TDEE |
| Device Readout | Vendor algorithm | Only if you keep the same device and settings |
Worked Examples You Can Copy
Example 1: 60-Kg Adult, 7.5 Hours
MET method: 60 × 7.5 ≈ 450 kcal. BMR share: if Mifflin outputs 1350 kcal/day, then 1350 × 7.5/24 ≈ 422 kcal.
Example 2: 82-Kg Adult, 8 Hours
MET method: 82 × 8 ≈ 656 kcal. BMR share: if Mifflin outputs 1750 kcal/day, then 1750 × 8/24 ≈ 583 kcal.
Example 3: 95-Kg Adult, 6.5 Hours In A Cool Room
MET method: 95 × 6.5 × 1.03 ≈ 636 kcal with the small temperature nudge used in the widget. BMR share: if BMR is 1900 kcal/day, then 1900 × 6.5/24 × 1.03 ≈ 528 kcal.
How To Get A Figure You’ll Trust
Pick one method. Use it every night for two weeks. Note your hours and the number you get. Consistency beats perfection.
Track a few context cues. Room temperature, late meals, and training days explain many swings. A simple note is enough.
Pair night math with day steps. A short walk after dinner or a few sets of push-ups changes your basal picture over months, not just days. If you’re starting fresh, you’ll like the structure in the easy steps to healthier life.
Glossary For Quick Scanning
MET. A unit that compares an activity to resting energy use. Sleep sits at 1.0.
BMR. An estimate of calories your body needs for basic functions over a day of rest. The Mifflin-St Jeor equation is common in clinics and coaching.
RMR. A closely related measure that relaxes lab rules. For home planning, it’s often treated the same way as BMR.
References Linked Inside The Article
For MET values and the definition of 1.0 during sleep, see the activity compendium’s inactivity list. For converting METs to calories across tasks (and the general formula that underpins the first method), Texas A&M’s extension guide offers a friendly walkthrough. If you prefer a day-wide target, the NIH Body Weight Planner is a good next step for setting intake and activity in one place.