# Power-to-Weight Ratio Calculator

Engineers will find our power-to-weight ratio calculator a handy tool to measure the **performance of an engine**.

In this article, you will learn:

- What is the power-to-weight ratio?
- How to calculate the power-to-weight ratio?
- How does the power-to-weight ratio affect the performance of a vehicle?

## What is the power-to-weight ratio?

The **power-to-weight ratio** is a **vehicle specification** which somehow **uniforms** the comparison of the performance of a vehicle-engine pair.

The ability of an engine to supply a vehicle with acceleration and speed is measured in **power**. The power of an engine is assimilable to the **energy output per unit of time**: we can measure it in **watts** or, traditionally, in **horsepowers**.

The power, however, is not everything. Put the engine of a Dodge Viper on a Reliant Robin, and you will easily understand why!

## How do I calculate the power-to-weight ratio formula?

To calculate the power-to-weight ratio, be sure to know:

- The
**weight****of the vehicle**$W$; and - The
**power of the engine**$P$.

The formula for the power-to-weight ratio is simple:

As you can see, the **weight** of the vehicle is at the denominator: the **heavier the vehicle**, the lower the power-to-weight ratio. The same effect comes from a lower power.

A lower $\text{PWR}$ gives the platform worse performances. If you want a car that accelerates quickly and goes fast, check for **higher values** of power-to-weight ratio.

🙋 You can calculate the power-to-weight ratio also using the engine's weight, though this will not give you all the information about the vehicle's performance.

## Not only cars: how to measure the power-to-weight ratio in different situations

The power-to-weight ratio is not exclusive to cars or motorcycles. Since moving from one place to another requires performing **work** (in the physical sense) — that is **energy** — in a given time, we can define a **power**.

**You** have a power-to-weight ratio. It doesn't really matter when you are walking in the city, but the moment you don a backpack and head for the mountain, it **does matter**! That's why you want to pack light. The same holds for running: look at how lean is a marathon runner compared to a sprinter.

We can apply the power-to-weight ratio to cycling, too: it's even easier to calculate: To measure the power-to-weight ratio of a cyclist, you only need a

and a scale!Planes, rockets, and helicopters all have a power-to-weight ratio, though it's common to express the performance of flying vehicles using the **lift-to-drag ratio** or the **thrust-to-weight ratio**.

## Examples of power-to-weight ratio calculations in real life

Now that you know how to calculate the power-to-weight ratio let's see some examples where we can apply the formula for the power-to-weight ratio.

- A
**DeLorean****DMC-12**(the car of*Back to the Future*), has a weight of $1,233\ \text{kg}$ (or $2,718\ \text{lb}$), and a power output of $130\ \text{hp}$ ($97\ \text{kW}$), which gives it a power-to-weight ratio of $78.7\ \text{kW}/\text{kg} = 0.0479\ \text{hp}/\text{lb}$. - The two engines of a
**Boeing 777**, the GE 90-115B supply a power of $23\ \text{MW}$ ($30,844\ \text{hp}$). The maximum weight of the plane is $299,370\ \text{kg}$ or $660,000\ \text{lb}$. The power-to-weight ratio we calculate is... $76.8\ \text{kW}/\text{kg}$: The same as the DeLorean! - A $70\ \text{kg}$ cyclist in a really good shape can produce easily $200\ \text{W}$ of power. The power-to-weight ratio is $2.6\ \text{W}/\text{kg}$. Lance Armstrong, by comparison, is assumed to have produced more than $7\ \text{W}/\text{kg}$ at his peak performance. Look at the difference between planes and cyclists, but remember: two wheels and pedals are the best way to move!