You can't give a single answer to "What is the length of an asteroid?" because asteroids come in a wide variety of sizes. Here's why:

* Vast Size Range: Asteroids range from tiny pebbles to massive objects hundreds of kilometers across.

* Irregular Shapes: Most asteroids are not perfectly spherical, so their "length" can be hard to define. They can be elongated, potato-shaped, or even have multiple lobes.

* Variable Measurement: Depending on the asteroid's shape, we might measure its longest dimension, its average diameter, or its volume.

Here are some examples to give you an idea of the size range:

* Ceres: The largest asteroid in the asteroid belt, with a diameter of about 946 kilometers (588 miles).

* Vesta: Another large asteroid, with a diameter of about 525 kilometers (326 miles).

* Eros: A smaller asteroid, about 33 kilometers (21 miles) long and 13 kilometers (8 miles) wide.

* Itokawa: A tiny asteroid, only a few hundred meters across.

To find the length of a specific asteroid, you would need to look it up in a database of asteroids. There are online resources that provide information about asteroid size, shape, and other properties.