E-Bike Power Explained: Watts, Volts, Amp Hours, Watt Hours & Torque (Nm)

When shopping for an electric bike or planning a conversion, you’ll come across terms like watts, volts, amp hours, watt hours, and torque. These numbers are often used in marketing – but what do they actually mean? And which ones really matter?

In this guide, we break down the key specs so you can make smarter choices when comparing motors, batteries, and performance – especially when deciding between a mid-drive or hub motor setup.

Watts (W): The Motor's Power Rating

Watts refer to the power output of the motor.

• A 250W motor is road legal in the UK and ideal for commuting or casual riding.

• A 500W or 750W motor offers more acceleration and climbing power (used off-road or on private land).

• Higher wattage generally means more power – but it’s not the whole story.

🧠 Mid-drive advantage: Mid-drive motors often feel more powerful than hub motors with the same wattage because they drive through the gears, making better use of torque and cadence.

Volts (V): The Battery's Pressure

Think of voltage like water pressure in a hose. Higher voltage = more potential power.

• Common e-bike voltages: 36V, 48V, and 52V

• Higher voltage can:

  • Deliver more power to the motor

  • Reduce heat in the wiring

  • Improve efficiency (if the motor is designed for it)

🧠 Mid-drive tip: Mid-drives usually benefit more from higher voltage systems, as they use it more efficiently to climb hills and carry loads.

Amp Hours (Ah): Battery Capacity

Amp hours tell you how much energy the battery can store. It’s like the size of your fuel tank.

• A 10Ah battery can deliver 10 amps for one hour, or 1 amp for 10 hours.

• The higher the Ah, the longer your range – assuming all else is equal.

🧠 Mid-drive motors are generally more efficient, so you can often get more range from the same battery size compared to a hub motor.

Watt Hours (Wh): The Real Range Number

Watt hours = Voltage × Amp hours. This is the most accurate way to measure how far a battery will take you.

Example battery setups:

Voltage	Amp Hours	Total Watt Hours
36V	10Ah	360Wh
36V	17.5Ah	630Wh
36V	20Ah	720Wh
48V	10Ah	480Wh
48V	17.5Ah	840Wh
48V	20Ah	960Wh

A larger Wh figure means the battery can store and deliver more energy, giving you greater range – depending on assist level, terrain, rider weight, and conditions.

🧠 Mid-drives make better use of watt-hours compared to hub motors, especially in hilly or stop-start environments.

Amps (A): Flow of Power

Amps measure the flow of current from the battery to the motor.

• The controller limits how many amps can flow at once (e.g. 15A, 25A, etc.)

• Higher amps = more torque and acceleration, but also more heat and battery drain

🧠 Unlike most hub systems, mid-drive controllers are usually better tuned and matched to the motor, giving you a smoother, more responsive pedal assist experience.

Torque (Nm): How Strong the Motor Feels

Torque is measured in Newton-metres (Nm) and tells you how much twisting force the motor applies – basically, how quickly it can get you moving or up a hill when pedalling.

• Low-torque motors (e.g. 30–40Nm) feel gentle and are fine for flat terrain.

• Mid-torque (50–70Nm) is good for most riders and commutes.

• High-torque (80–120Nm) is ideal for steep hills, heavier riders, or towing.

🧠 Mid-drives produce significantly more torque than hub motors at the same watt rating – making them the clear winner for hills, towing, and off-road riding.

🤯 Still Confused? Here’s a Quick Analogy

Imagine your e-bike system is like a car:

Spec	Analogy
Watts	Horsepower – how powerful the motor is
Volts	The fuel pressure – how fast power can be delivered
Amps	The fuel flow – how much power is delivered at once
Amp Hours	Size of the fuel tank
Watt Hours	Total driving range
Torque	How responsive it feels when you press the pedals

🧠 Bonus analogy: A hub motor is like a single-speed scooter – decent on the flat, but not great on hills. A mid-drive is like a geared motorbike – efficient, powerful, and responsive across all terrain.

Why It’s Not Just About the Numbers

We’ve worked on hundreds of conversions – and we can tell you this:

Two bikes with “250W” motors can feel completely different.

Why?

• Some batteries can’t deliver enough current

• Some controllers are underpowered or poorly tuned

• Some kits use cheap components that underperform despite the “specs”

At E-MY-BIKE, we focus on real-world performance. We only install quality systems – usually mid-drives – that are built to last, tuned properly, and fitted with safety and rideability in mind.

Want Help Choosing the Right Setup?

Whether you’re planning a conversion or already have an e-bike and want to upgrade, we’re here to help.

👉 [Contact us now] for advice, quotes, or a custom build tailored to your riding style and terrain.