Miles per gallon for short journeys?

A few days ago I had to run my friend to the station which was a round trip of about 3 miles. This made me wonder how many miles per gallon would a cold engine normally expect to be able to do?

The data in my case is below. Would something like 40% or 50% of what a warmed up engine be a reasonable guess?

Thanks for any thoughts.

Svend

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10 year old Mazda 323. 1.3 litre carburettor engine.

With a fully warmed up engine I can usually measure about 40 miles to the gallon on a long motorway journey

With a fully warmed up engine I *guess* I might probably get about

18 miles per gallon in town.

I suspect that my car's engine doesn't truly warm up until it has done about 5 miles although the engine behaves as if it has warmed up after only about 3 miles.