Mooney M20M pilot reported a rough running engine; followed by complete power loss; due to fuel mismanagement and starvation. The aircraft was able to land safely; without power; at a nearby airport.

Narrative

I advised ATC when the engine faltered. I turned on boost pump and engine smoothed. After a short period I turned off the boost pump and engine continued OK. However; in another minute or so; engine faltered more seriously. I requested priority handling and ATC vectored me to ZZZ; where I landed safely without power. After lengthy phone consultation with my Mechanic he believed I had a fuel quality or supply issue. Upon investigation I found I had run a tank dry.How did this happen? This aircraft is heavy; with only 840lbs useful load. In addition; it has STC's extra fuel capacity of 118 gallons (708lbs). As a result; we (aircraft owned with others) try to fill to 60 gallons. The only way to measure this is with strapping tables supplied by the previous owner. I was about to switch tanks when this incident occurred; believing there was 5 gallons in the left tank. After requesting priority handling; I did switch tanks but when that didn't provide an immediate fix I switched back to the tank that later proved to be empty. This was a mistake---I should have realized there could be vapor in the line. In my defense; I never considered I had an empty tank. When I added fuel at ZZZ; I learned that the strapping table for that tank was 2-3 gallons high.This incident has prompted much discussion among the owners. We will all be more conservative in fuel planning and monitoring. It has raised an issue of whether the JPI (J.P. Instruments) fuel totalizer is reading a gallon or so too low. We use that to add fuel at the end of a flight and any error could accumulate; though not to a large amount because of the cross check provided by the strapping table. Life was simpler when we had a Bonanza and filled the tanks after each flight.