Lice are tiny insects, measuring just a few millimeters in length. Their weight is extremely small, typically in the range of a few milligrams.
It's practically impossible to weigh a single louse accurately, as it would require specialized equipment and a very sensitive scale. However, you can get an idea of their size by comparing them to a grain of rice or a pinhead.
While the weight of individual lice is negligible, a heavy infestation can cause significant health problems for your dog, including hair loss, skin irritation, and even secondary bacterial infections.