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E-bike range versus battery capacity: how Wh becomes miles

Watt-hours put an upper limit on how far a battery can take you, but the distance you actually get depends on how much energy the ride demands per mile.

Range starts from watt-hours

Because watt-hours measure stored energy, they set the ceiling on range. A larger watt-hour pack always has the potential to go further on the same bike. This is why comparing packs by watt-hours, rather than amp-hours, is the only fair way to judge range potential.

Turning watt-hours into a distance needs a consumption figure in watt-hours per mile. Divide the pack's watt-hours by that consumption and you get an estimated range.

What consumption depends on

Consumption per mile is dominated by assist level. The highest support setting can use two to three times the energy of the lowest eco setting, which is why the same battery can cover a very wide range of distances. Rider and cargo weight, headwind, hills, tyre choice and how fast you ride all push consumption up or down.

A commonly used span for a mid-drive bike is roughly 7 to 20 watt-hours per mile. Riding gently on the flat sits near the low end; heavy assist up hills sits near the high end.

Worked examples

A 500Wh pack at 10 watt-hours per mile gives about 50 miles; at 20 watt-hours per mile it gives about 25 miles. A 625Wh pack at the same rates gives roughly 62 and 31 miles. The pattern holds: doubling consumption roughly halves range, and a bigger pack shifts the whole span up.

This is why manufacturers publish a range span rather than a single number, and why a real-world estimate should always assume your own typical assist level and terrain.

Extending range without a bigger pack

Lower assist levels, higher tyre pressure within the tyre's rating, less cargo and a steadier speed all cut consumption and extend range from the same battery. A range-extender pack, where the system supports one, adds watt-hours in parallel and directly increases the ceiling.

Related

Sources: Bosch eBike Systems range documentation · Shimano STEPS range and efficiency data