I made my own: https://observablehq.com/@andyreagan/bmr-calculator

• https://www.omnicalculator.com/sports/vo2-max
• https://www.omnicalculator.com/sports/steps-to-calories

Has good notes on their API.

> Considerations > If a user hasn't synced a tracker for more than seven (7) days, the tracker stores only summary values for the days older than one week. In this case, the intraday data for steps is zero and the intraday calories are calculated from BMR or EER. Intraday steps could be estimated from the total daily summary data by the equation above. > For the current day we will include only values until current timestamp (in the user's timezone). > If a specific time interval was passed to the call via start-time/end-time parameters, data-value will include a summary only for the requested time period (versus whole day). > For the activities/log/calories resource, each data point also includes the level field that reflects calculated activity level for that time period ( 0 - sedentary; 1 - lightly active; 2 - fairly active; 3 - very active). > If BMR or EER have been used to estimate calories for the whole specific day (no tracker data), intraday data for calories would be flat and estimated according to the simple equation calories_1m = BMR(EER)/24/60. > Using BMR/EER Algorithms > If a user had no Fitbit tracker data for the specific day then the greater of Logged Activities + BMR (for minutes when there is no activity) and the calories calculated from the EER for that day (if EER enabled for this user's profile) are taken. In case, there was some data from the tracker for the specific day, that data where available is used and for time where data is unavailable, the BMR is used. If the total is less than 20% greater than BMR then the EER (cals < EER * 0.8) is used. EER never used to calculate calories for today. > > Using BMR Formula > Fitbit uses the standard MD Mifflin-St Jeor equation: > > 9.99 * weightKg + 6.25*heightCm - 4.92*ageYears + s, where s is +5 for > males > and -161 for female > EER Formula (TEE total energy expenditure) > The EER Formula is based on http://www.cdc.gov/pcd/issues/2006/oct/pdf/06_0034.pdf, which in turn is based on "Food and Nutrition Board. Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids (macronutrients). Washington (DC): National Academy Press; 2005." http://www.nap.edu/openbook.php?isbn=0309085373&page=204 > > MALE-based EER Formula: > TEE = 864 - 9.72 x age (years) + 1.0 x (14.2 x weight(kg) + 503 x height > (meters)) > FEMALE-based EER Formula: > TEE = 387 - 7.31 x age (years) + 1.0 x (10.9 x weight(kg) + 660.7 x height > (meters))