On an e-bike, watts measure power (how hard the motor pushes), volts set how fast the motor can spin, amps control the punch it delivers off the line, and watt-hours tell you how far the battery will take you. Power in watts is simply volts × amps — so a 48V battery feeding 20 amps is delivering roughly 960 watts. But here’s the catch the whole industry glosses over: there is no standard way to rate an e-bike motor’s wattage, which is exactly why the same motor gets sold as “250W” by one seller and “1000W” by another. At Cyberbikes in Leichhardt we get asked what these numbers mean every week, so let’s decode them properly — with help from the engineers at Grin Technologies (ebikes.ca), one of the most respected e-bike engineering crews in the world.
The 60-second version: watts, volts, amps and watt-hours
Four specs do all the heavy lifting on an e-bike spec sheet. Here’s what each one actually controls:
| Spec | Unit | What it controls | Plumbing analogy |
|---|---|---|---|
| Voltage | Volts (V) | How fast the motor can spin — your top speed | Water pressure |
| Current | Amps (A) | Torque and acceleration — punch off the line and up hills | Flow rate |
| Power | Watts (W) = V × A | Total push the system delivers at any moment | Water coming out right now |
| Energy | Watt-hours (Wh) = V × Ah | How far you can ride — your range | Size of the tank |
Keep that table in mind and 90% of e-bike marketing suddenly makes sense. The two numbers riders fixate on — motor watts and battery volts — are also the two most misunderstood. Let’s take them apart.
Why “250W” doesn’t mean what you think
Here’s the uncomfortable truth from the engineers at ebikes.ca: there is no standardised method for rating an e-bike motor’s power in watts. A 60-watt lightbulb draws 60 watts — simple. But an electric motor doesn’t produce a fixed power when you switch it on. Spin it with the wheel off the ground and it makes almost no power; load it up a hill and its output climbs, then falls again as it slows. The actual output depends entirely on how hard it’s working and how much current the controller lets through — not on a number printed on a sticker.
So where does the headline wattage come from? Usually it’s the peak input power — volts × amps measured at the controller — which is the biggest, most marketable number available. The real mechanical power reaching the road is typically around 30% lower once you account for efficiency losses. As Grin puts it, a kit advertised as “3600W” (a 72V battery × 50A controller) might only ever put out around 2000W of actual mechanical power, and can sustain far less than that without cooking itself.
That last point matters. It’s not watts that destroy a motor — it’s torque, and the current that creates it. Double the current through the motor windings and you get double the torque, but four times the heat (the I²R relationship). Push too hard for too long and the enamel burns off the copper, gears soften, or magnets demagnetise. That’s a “cooked” motor.
The kicker: peak power is mostly a property of the battery and controller, not the motor. ebikes.ca ran the same hub motor three ways — at 36V/20A it peaked around 600W output; with a 40A controller, about 1058W; and at 52V/20A, about 840W but with a much higher top speed. Same motor, wildly different “power”. You can explore this yourself with Grin’s excellent online motor simulator. The practical takeaway for a buyer: don’t shop on the headline watt number. In NSW, road-legal e-bikes are capped at 500W (dropping to 250W with EN 15194 certification from 1 March 2029) continuous pedal-assist to 25 km/h regardless, so a sensibly-tuned 250W system is exactly what you want.
Volts vs amps: which one makes you faster?
This is the question behind half the “is 48V better than 36V?” searches. The short answer: volts buy you speed, amps buy you grunt.
A motor spins at a rate set by its winding and the voltage you feed it — more volts, more RPM, higher top speed. That’s why the ebikes.ca 52V example kept accelerating past 55 km/h while the 36V version topped out earlier. Amps, on the other hand, feed torque: a higher-current controller gives sharper acceleration off the line and more pulling power on steep hills, but it won’t raise your top speed. This is why a 36V/40A setup feels punchy from a standstill but no faster at cruise, while a 52V/20A setup feels a touch softer off the line yet pulls away to a higher speed.
For everyday Sydney commuting, 48V is the sweet spot — enough voltage for confident hills and headwinds, without the weight and cost of a high-voltage pack. Our Centauro runs a 48V system for exactly that reason.
Watt-hours and range: how far will it actually go?
Watt-hours (Wh) are the single most useful number on the whole spec sheet, because they tell you the size of your “fuel tank”. The formula is simple: Wh = volts × amp-hours (Ah). The Centauro’s 48V 25Ah Samsung battery holds 48 × 25 = 1,200Wh of energy.
To turn that into distance, divide by how much energy you burn per kilometre. A typical e-bike uses roughly 7–15 Wh/km depending on assist level, rider weight, hills and wind. So 1,200Wh ÷ 10 Wh/km ≈ 120 km of gentle-assist riding, or ÷ 15 ≈ 80 km when you’re working it harder. That range — not a single hero number — is why any honest shop quotes a window. If you want to model your exact route and rider profile, Grin’s trip simulator is the gold standard.
See a real e-bike motor up close
Numbers are easier to trust when you can see the hardware. Our crew filmed a full mid-drive motor installation so you can see exactly where the torque and power come from — the motor, the controller, and how it all bolts to the frame:
Seeing an error code instead of a spec sheet? Our quick “Bafang Error 30 — Fix It Fast” video walks you through the most common motor-signal fault in under a minute. It’s the kind of thing our @cyberbikesau channel is full of, because we’d rather you understood your bike than feared it.
Frequently Asked Questions
Is a 500W e-bike better than a 250W one?
Not necessarily. Because there’s no standard watt rating, a “500W” motor from one brand can perform like a “250W” from another. What matters is the combination of battery voltage, controller amps and motor quality — and in NSW, road-legal pedal-assist e-bikes are limited to 500W continuous and 25 km/h anyway. A well-tuned 250W system is plenty for city and hill riding.
Does higher voltage make an e-bike faster?
Yes — voltage largely determines how fast the motor can spin, so a higher-voltage pack (say 52V vs 36V) raises top speed. Amps, by contrast, control acceleration and hill-climbing torque, not top speed. For most Sydney commuters, 48V balances speed, weight and cost well.
How do I calculate my e-bike’s range from watt-hours?
Multiply battery volts by amp-hours to get watt-hours (e.g. 48V × 25Ah = 1,200Wh), then divide by your energy use per kilometre. Most e-bikes consume 7–15 Wh/km, so a 1,200Wh battery delivers roughly 80–120 km depending on assist level, terrain, rider weight and wind.
Why are e-bikes limited to 500W in NSW?
NSW law defines a road-legal electric bike as a pedal-assist (pedalec) bike with a motor rated up to 500W continuous that cuts assistance at 25 km/h. Higher-powered bikes are classed differently and generally aren’t legal for footpaths, shared paths or roads without registration. It’s why our Centauro is built to the 250W, 25 km/h standard.
Want to feel the difference between watts, volts and amps for yourself? Come in for a test ride at Cyberbikes, 281 Parramatta Road, Leichhardt — our crew will happily geek out on motor specs with you. Call us on 0491 794 668 or browse the range at cyberbikes.com. Ask about rent-to-own from $99.99/week.
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