Generally, you would use the COMMUTED VALUE of your pension -- if you quit today, what cash would be paid out to you?
Before vesting, it is typically your contributions plus interest (but not including the employer portion). Most pensions here have required employee contributions, often up to 9% of base salary.
After vesting, commuted value depends on your age and how / why you are withdrawing. It could be the employer + employee contributions, or the formula for what you would be entitiled to if you retired today, as a lump sum. e.g., what cash would you receive to be ported to a locked in or another retirement account if you quite? It is not a lot until you hit your 40's, because of time value of money.
If you qualify for early retirement, and leave your job, some pensions only pay out the discounted early retirement amount.
If you are vested - you need to ask your benefits group for your commuted value number. They don't like doing these too often, unless you are nearing retirement, though!