The word "crust" can refer to several things, so the measurement will depend on what you're talking about. Could you please be more specific? For example, are you asking about:

* The Earth's crust? It's measured in kilometers (km) and ranges from about 5 km (3 miles) thick under the oceans to around 70 km (43 miles) thick under continents.

* The crust of a pie? It's measured in millimeters (mm) or centimeters (cm) and can vary depending on the recipe.

* The crust of bread? It's measured in millimeters (mm) or centimeters (cm) and is typically a few millimeters thick.

Please clarify your question so I can give you the most accurate answer.