That's an easy one.

Paris to Le Havre, Le Havre to [I assume you plan on seeing] the beaches at Normandy and the American Cemetery, from there to Avranches and Mont Saint Michel [having an omelette at Le Mere Poulard of course] then from Mont Saint Michel to Chartres and then back to Paris.

It is about a 2-hour 121 mile drive from central Paris to Le Havre, about a 70 mile, hour-and-a-half drive from Le Havre to Vierville/St. Laurent [American Cemetery].

From Vierville to Cherbourg it is about a 50 mile one-hour drive and then another 170 mile drive from Cherbourg to Creances to Avaranches/Mont Saint Michel.

From Mont Saint Michel to Chartres is a 210 mile, 3.5-hour drive and another 55 mile, 1-hour drive from Chartre to central Paris.

Including plenty of time to makes stops along the way this is an easy +/- 450 mile circle that can be done comfortably in two days or at a very relaxed pace in three. It will also make for an unforgettable side trip.