About

Cycling energy expenditure varies drastically between stationary environments and outdoor terrain. Generic calculators often fail because they treat a 15mph ride on a flat road the same as a 15mph ride into a headwind. This tool addresses that discrepancy by separating logic for Outdoor (MET-based) and Indoor (Watt-based) cycling.

For outdoor cyclists, the calculation utilizes Metabolic Equivalent of Task (MET) values derived from the Compendium of Physical Activities, categorized by effort zones (Drafting, Leisure, Racing). For indoor training, accuracy is significantly higher when utilizing power output. The tool converts average wattage directly into caloric burn using the laws of thermodynamics and human mechanical efficiency.

Formulas

1. Outdoor (METs):
The standard caloric expenditure formula is applied based on velocity and effort tiers:

Kcal = MET × Weight_kg × Time_hr

2. Indoor (Watts):
Using power output creates a direct link between mechanical work and chemical energy. We assume a gross mechanical efficiency (GME) of roughly 24% (1 kcal ≈ 4.18 kJ).

Kcal = AvgWatts × Time_hr × 3.64.18

Reference Data

Intensity	Speed (mph)	Speed (km/h)	Watts (Est.)	METs
Leisure (Slow)	< 10	< 16	< 100	4.0
Moderate (Light)	10 - 12	16 - 19	100 - 130	6.8
Moderate (General)	12 - 14	19 - 22	130 - 160	8.0
Vigorous (Fast)	14 - 16	22 - 26	160 - 200	10.0
Vigorous (Very Fast)	16 - 19	26 - 31	200 - 250	12.0
Racing (Drafting)	> 20	> 32	varies	8.5
Racing (No Draft)	> 20	> 32	250+	16.0
Mountain (Uphill)	Any	Any	300+	14.0

Frequently Asked Questions

Drafting behind another cyclist or vehicle reduces aerodynamic drag by up to 30-40%. Since air resistance is the primary force opposing a cyclist at speed, removing it drastically lowers the power (and calories) required to maintain velocity.

Yes, significantly. METs are statistical averages based on speed, but they cannot account for wind, tire pressure, or road gradient. Watts measure the actual mechanical force you apply to the pedals. If your stationary bike reports Watts, always use that mode.

In the Outdoor formula, weight is a direct multiplier because moving heavier mass requires more energy. In the Watt-based formula, weight is implicitly factored into the power you produce (it takes more watts to move a heavier body), so it is not a direct variable in the conversion equation.

The threshold is typically around 14 mph (22 km/h). Below this speed, wind resistance is manageable. Above this, drag increases exponentially, requiring a disproportionate increase in energy output (METs jump from 8.0 to 12.0).