"How far will it go?" is the first question almost everyone asks about an electric conversion, and it's also the one with the most slippery answer. Range isn't a fixed number stamped on the battery; it's the result of how much energy you carry and how fast you spend it, and the spending rate depends on you, the bike, the road and the weather. The reassuring news is that the underlying maths is simple, and once you understand it you can estimate your own range with reasonable confidence and, better still, learn how to stretch it. This guide explains how range is calculated, what changes it, what's realistic for different battery sizes, and why the figure on the advert is usually optimistic.

If you'd rather just get a quick number for your own setup, the range estimator on the Convert.bike home page lets you plug in your battery size and assist style and see a sensible estimate in seconds. Use it alongside this guide so the figure actually means something to you.

How range is calculated

Range comes down to one tidy equation: range = battery energy (Wh) ÷ energy use per kilometre (Wh/km). Battery energy is measured in watt-hours, and you'll usually find it printed on the pack or worked out from volts multiplied by amp-hours (for example, 36 V × 10 Ah = 360 Wh).

The second half, consumption, typically lands somewhere between 7 and 20 Wh per kilometre for a conversion. A light rider on the flat, pedalling hard with low assist, might sip around 7–10 Wh/km. A heavier rider on hills, using high assist or a throttle, can easily push toward 18–20 Wh/km or more. So a 360 Wh battery might give roughly 360 ÷ 10 = 36 km in efficient use, or 360 ÷ 18 = 20 km when worked hard. Same battery, nearly double the difference, purely from how it's ridden. To understand the battery side of this in more depth, see the e-bike conversion battery guide.

What changes your consumption

Several factors push your Wh/km up or down, and they stack together.

Rider and cargo weight

More total weight takes more energy to accelerate and climb. A heavier rider, panniers, or a child seat all raise consumption, most noticeably on hills and from a standing start.

Terrain

Hills are the single biggest variable. Climbing demands far more energy than rolling along the flat, and while you recover a little on descents, you never get it all back. A hilly route can slash range compared with the same distance on level ground.

Wind

Air resistance grows quickly with speed, so a stiff headwind behaves a lot like a permanent gentle hill. A tailwind helps, but as with descents, the saving rarely matches the cost of the headwind on the way out.

Assist level and throttle versus pedalling

This is the factor you control most. High assist levels and using a throttle (where the motor does the work and your legs don't) drain the battery fastest. Pedalling meaningfully and keeping assist modest can dramatically extend range, because every watt your legs contribute is a watt the battery keeps.

Temperature

Batteries deliver less usable energy in the cold. A winter ride can noticeably shorten range compared with the same trip in mild weather, and the pack also charges best at moderate temperatures.

Tyres and pressure

Under-inflated or very knobbly tyres increase rolling resistance and waste energy. Keeping tyres at a sensible pressure for your weight is one of the easiest free range gains there is.

Stop-start riding

Every time you accelerate from a stop you spend energy getting back up to speed. A flowing rural route is far kinder to range than stop-start city traffic with frequent lights and junctions, where you're constantly paying that acceleration cost again. Average speed matters too: pushing along near your assist limit burns energy faster than cruising at a relaxed pace, partly because of air resistance and partly because the motor spends more time working hard.

It's worth stressing that these factors compound rather than simply adding up. A heavy rider, into a headwind, up a hill, on soft tyres, in the cold, using full throttle will see consumption at the very top of the range, while flip every one of those and the same battery can travel two or three times as far. That's why two riders with identical kits can report wildly different range, and neither is wrong.

Realistic range bands by battery size

With consumption of roughly 7–20 Wh/km, here are sensible real-world expectations. Treat these as estimates, not promises, because your own numbers depend on everything above.

  • Small battery, around 250–350 Wh: roughly 15–45 km. Fine for short commutes and errands, especially if you pedal and keep assist low.
  • Mid-size battery, around 400–500 Wh: roughly 25–65 km. The popular all-rounder, comfortable for most daily riding with a margin to spare.
  • Large battery, around 600–700 Wh: roughly 35–90 km. Suited to longer commutes, hilly areas, heavier riders, or anyone who likes high assist.
  • Very large or dual-battery setups, 800 Wh and up: 50–120 km or beyond, for touring and serious distance.

Notice how wide each band is. That spread is the honest reality of e-bike range, and it's why a single advertised figure can never tell the whole story. When you're sizing a battery, a good approach is to estimate the longest regular ride you'll do, work out the energy it needs at a realistic Wh/km for your weight and terrain, and then add a comfortable margin so you're never nursing a flat pack home. It's far better to carry a little spare capacity than to run out a few kilometres from your door.

How to extend your range

If you want more kilometres from the battery you already have, the levers are practical and cheap:

  • Pedal more and assist less. Dropping a notch on the assist level is the biggest single saving you can make on the move.
  • Use the throttle sparingly. Let it help you pull away, then ease off and let your legs share the load.
  • Keep tyres properly inflated and choose smoother tyres if your riding allows.
  • Ride smoothly. Anticipate junctions and coast where you can, rather than braking hard and re-accelerating.
  • Look after the battery. Store and charge it at moderate temperatures, and bring it indoors before a cold-weather ride.
  • Trim unnecessary weight from racks and bags you aren't using that day.

None of these require new parts; they simply lower your Wh/km so each charge goes further.

Why advertised ranges are optimistic

Headline range figures are usually generated under ideal, gentle conditions: a light rider, flat ground, no wind, warm weather, low assist and steady pedalling. Real riding involves hills, headwinds, traffic, cold mornings and the temptation to use more assist than you planned. That's not necessarily dishonest, it's a best-case number, but it's why your actual range often lands well below the quoted one. A useful rule of thumb is to expect the middle of the relevant band for normal riding, and the lower end if you ride hard or live somewhere hilly. Building a budget around real costs is much the same: see the cost to convert a bike to electric for sensible, real-world figures rather than headline ones.

Next steps

The best way to know your true range is to ride a known loop, watch how much battery you use, and work backwards to your own Wh/km, then size future batteries around that. Try the home-page range estimator for a quick starting figure, then read the e-bike conversion battery guide to choose the right capacity, and revisit the complete guide to converting a bike to electric to see how battery choice fits the wider build. Understand the simple Wh ÷ Wh/km maths, ride a little more efficiently, and your conversion will go further than the spec sheet suggests.