Keep time units consistent
Speed formulas require matching units. If speed is miles per hour, time must be in hours, not minutes, unless you convert first.
For example, 30 minutes is 0.5 hours. Forgetting that conversion doubles or halves many travel estimates.
Use average speed realistically
A route with traffic lights, border checks, hills, weather, and breaks will not match a constant-speed calculation.
Use calculator results as a planning baseline, then add buffer for stops, delays, loading, parking, or schedule changes.
Avoid precision that looks false
A conversion can produce many decimal places, but travel plans rarely deserve that precision. Rounding to practical minutes or tenths of a mile is usually clearer.
For safety, obey posted speed limits and local travel advisories instead of relying on a calculated average.