Mensura

How it works: Choose a measurement system and a topic, then convert each changing question before the timer runs out. Each question gives four choices; get at least 7 of 10 right to win.

Score and best result: Correct answers earn points, with a small speed bonus. Metric, US customary and British Imperial units are kept distinct. Your best is saved by system, topic and level; high scores rank by points, with time as the tie-breaker.