This depends on your industry, company culture and office protocol. If you work in fashion for example, you have more flexibility and go for the staggering heights of a 4-inch or more heel. But for most offices I would generally recommend 2.5 - 3 inches maximum -- anything more might be interpreted as too sexy or overkill. Most important, you must consider your own comfort zone. If you're on your feet all day, you might opt for a shorter heel to keep your feet happy. If you get to sit all day, it's a lot easier to wear the higher heels.