Smartwatch Calorie Accuracy
Reviewed by Sameer Sontakey, Co-founder and Chief AI & Algorithms Officer at Sensor Bio. ChatPPG is independent and device-neutral; it is not a Sensor Bio product.
No wearable counts calories accurately. Against indirect calorimetry, Shcherbina 2017 found no device with an energy expenditure error below 20%, and two later studies reported coefficients of variation of 8.0% to 34.5% for Apple, Polar, Garmin and Fitbit watches.
Which wearable is most accurate for calories?
22 published results from 10 studies in the wearable accuracy database. Each ranking below compares devices only on the same statistic against the same kind of reference. Results from different statistics or references are never ranked together.
Evidence by brand
- Apple Watch6 studies, n = 247
- Oura2 studies, n = 21
- WHOOPNo published validation found
- Garmin3 studies, n = 96
- Fitbit4 studies, n = 189
- Pixel Watch1 study, n = 34No independent validation
- Samsung2 studies, n = 198
- Polar3 studies, n = 106
- WithingsNo published validation found
- AmazfitNo published validation found
- UltrahumanNo published validation found
- COROSNo published validation found
Energy expenditure (calories): mean absolute percentage error (%)
Reference: Indirect calorimetry. Lower is better. 2 studies; a device tested in more than one study shows its median.
- 1Huawei Watch GT 2e9.9%1 study, n = 20 (9.9% walk / 11.9% run) · Le et al. (2022)
- 2Google Pixel Watch 315%1 study, n = 34 (15.02%) · Lambe et al. (2026)Maker funded
- 3Apple Watch Series 619.8%1 study, n = 20 (19.8% walk / 24.4% run) · Le et al. (2022)
- 4Garmin Fenix 632%1 study, n = 20 (32.0% walk / 21.8% run) · Le et al. (2022)
Energy expenditure (calories): pearson correlation
Reference: Actiheart (ECG + accelerometer). Higher is better. 1 study.
- 1Oura Ring (Gen2)0.71 study, n = 21 (r = 0.70) · Henriksen et al. (2022)
- 2Polar Vantage0.691 study, n = 21 (r = 0.69) · Henriksen et al. (2022)
All published results
Every calorie result in the database, including statistics that cannot be ranked. Download the full table as CSV for all rows. From the wearable accuracy database (v1.0.0).
Energy expenditure (calories)10 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Oura Ring (Gen2)total energy expenditure | r = 0.70Pearson correlation | Actiheart / ActiGraph | n = 21, Free-living, up to 7 days | Henriksen et al. (2022)Independent |
| Polar Vantagetotal energy expenditure | r = 0.69Pearson correlation | Actiheart / ActiGraph | n = 21, Free-living, up to 7 days | Henriksen et al. (2022)Independent |
| Apple Watch Series 9 | Inconsistent across all groupsStudy finding (no single number) | Indirect calorimetry | n = 30, 10-min treadmill | Chase et al. (2024)Independent |
| Apple Watch Series 4 | 13.5%–27.1% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Polar Vantage V | 16.3%–28.0% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Garmin Fenix 5 | 15.9%–34.5% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Fitbit Versa | 8.0%–32.3% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Apple Watch Series 6 | 14.68–24.85% (poor in all activities)Coefficient of variation | Indirect calorimetry | n = 60, Sitting, walking, running, resistance, cycling | Hajj-Boutros et al. (2023)Funding not reported |
| Polar Vantage V | 16.54–25.78% (poor in all activities)Coefficient of variation | Indirect calorimetry | n = 60, Sitting, walking, running, resistance, cycling | Hajj-Boutros et al. (2023)Funding not reported |
| Fitbit Sense | 13.44–29.66% (poor in all activities)Coefficient of variation | Indirect calorimetry | n = 60, Sitting, walking, running, resistance, cycling | Hajj-Boutros et al. (2023)Funding not reported |
| Google Pixel Watch 3 | 15.02%Mean absolute percentage error | Indirect calorimetry | n = 34, Maximal treadmill test | Lambe et al. (2026)Maker funded |
| Oura Ring (Gen2) | r = 0.93 (lab)Pearson correlation | Indirect calorimetry | Laboratory activities | Kristiansson et al. (2023)Independent |
- Oura Ring (Gen2)r = 0.70
Pearson correlation, total energy expenditure · vs Actiheart / ActiGraph · n = 21, Free-living, up to 7 days
Henriksen et al. (2022) Independent
- Polar Vantager = 0.69
Pearson correlation, total energy expenditure · vs Actiheart / ActiGraph · n = 21, Free-living, up to 7 days
Henriksen et al. (2022) Independent
- Apple Watch Series 9Inconsistent across all groups
Study finding (no single number) · vs Indirect calorimetry · n = 30, 10-min treadmill
Chase et al. (2024) Independent
- Apple Watch Series 413.5%–27.1% (range by intensity)
Coefficient of variation · vs Indirect calorimetry · n = 25, Sitting, walking, running, sprints
Düking et al. (2020) Independent
- Polar Vantage V16.3%–28.0% (range by intensity)
Coefficient of variation · vs Indirect calorimetry · n = 25, Sitting, walking, running, sprints
Düking et al. (2020) Independent
- Garmin Fenix 515.9%–34.5% (range by intensity)
Coefficient of variation · vs Indirect calorimetry · n = 25, Sitting, walking, running, sprints
Düking et al. (2020) Independent
- Fitbit Versa8.0%–32.3% (range by intensity)
Coefficient of variation · vs Indirect calorimetry · n = 25, Sitting, walking, running, sprints
Düking et al. (2020) Independent
- Apple Watch Series 614.68–24.85% (poor in all activities)
Coefficient of variation · vs Indirect calorimetry · n = 60, Sitting, walking, running, resistance, cycling
Hajj-Boutros et al. (2023) Funding not reported
- Polar Vantage V16.54–25.78% (poor in all activities)
Coefficient of variation · vs Indirect calorimetry · n = 60, Sitting, walking, running, resistance, cycling
Hajj-Boutros et al. (2023) Funding not reported
- Fitbit Sense13.44–29.66% (poor in all activities)
Coefficient of variation · vs Indirect calorimetry · n = 60, Sitting, walking, running, resistance, cycling
Hajj-Boutros et al. (2023) Funding not reported
- Google Pixel Watch 315.02%
Mean absolute percentage error · vs Indirect calorimetry · n = 34, Maximal treadmill test
Lambe et al. (2026) Maker funded
- Oura Ring (Gen2)r = 0.93 (lab)
Pearson correlation · vs Indirect calorimetry · Laboratory activities
Kristiansson et al. (2023) Independent
10 more results in the database.
Read before comparing
- Calorie burn is modelled from heart rate, movement and your profile, not measured. Error changes with the activity: walking, running, cycling and weights differ.
- Studies report different statistics (percentage error, coefficient of variation, correlation, mean bias), so only like-for-like results are ranked.
- Rankings combine studies only when they report the same statistic against the same kind of reference, and still differ in protocol and population. Treat close values as ties.
Download the wearable accuracy table (CSV)
Every leaderboard row with study, DOI, reference standard and sample size. We'll email you the link.
FAQ
Which smartwatch is most accurate for calories?
None is accurate enough to rely on. In Le 2022, mean absolute percentage error while walking was 19.8% for Apple Watch Series 6 and 32.0% for Garmin Fenix 6. In Shcherbina 2017, no device achieved an error below 20%.
How large are smartwatch calorie errors?
In Kostrna 2026, a 10-minute cycling protocol against indirect calorimetry, mean bias was 21.60 kcal for Apple Watch Series 8, 68.61 kcal for Garmin Forerunner 955, 56.76 kcal for Samsung Galaxy Watch 5 and 3.14 kcal for Fitbit Sense 2, and error grew with body fat for every brand.