To talk about the physical distance from one side of something to the other,
we more often use wide.
- We live in a very wide street. The car’s too wide for the garage.
Broad can also be used in this physical sense, especially in more formal
- Across the broad valley, the mountains rose blue and mysterious.
- She wore a simple green dress with a broad black belt.
Note also: broad shoulders; a broad back; wide eyes; a wide mouth.
Wide is used in expressions of measurement: note the word order.
- The river is about half a mile wide. (NOT …
wide half a mile.)
Both words can express more abstract meanings.
broad agreement (= agreement on most important points)
broad-minded (= tolerant) broad daylight (= full, bright daylight)
a wide variety/range (of opinions etc)