If you have of can find a 3 or 4 year old
Red Book, use that to estimate the value of your collection. They are usually so far over in their prices, a few year old book would be more accurate.
However, only for usage if you wanted to buy them. As for selling your coins, use those prices and deduct about 25% for what you could sell them for.
However, selling really depends on how you do that. If you sell coins on
ebay, you should really get about what you tabulated the coins for. IF you took all your coins to a coin show and sold to a dealer there, you would probably get about 25% less than what you estimated the value at.
If you took your enire collection to a coin store, you would probably get an offer of about half of what you thought.
The real problem with using any coin guide for estimating your collections value is they all sort of list what you would or should pay to buy a coin, not sell one. And remember that many coins in a collection are considered just fillers to complete a set and by themselves are of little coin value.
You did say you only wanted to know what your collection is worth, not to sell it though. That too could make a difference. For almost anything you own, it is worth whatever you want it to be worth. Within reason of course.
A good example of this is how people are always told for insurance purposes, almost double what it is worth. That is since insurance companies usually only give you about half of what you lost or had stolen or damaged.
The real, hohest to goodnest, actual value of your coin collection is what you could sell it for.