What's a pawn worth?

Okay, I'm no longer blundering my pieces away so often anymore, and tend to be good - maybe too good(?) - to win material (a pawn or two), by move 15 or so. But I'm beginning to think it's time for me to stop being a pawn hunter, and that I need to learn when it's not worth it, taking a free pawn. Also, I need to learn when not to waste time defending my pawns (and maybe even pieces), at the cost of more important matters. 

So, can anyone give any guidelines about...

• a) ...what a pawn is worth (in terms of initiative, tempo, positioning and so on)? And, 
• b) ...how to know when to let a pawn go for something else. 

I think I've read that a pawn is worth 3 tempi. That's a lot, but I think I've seen plenty of examples of higher rated players giving up a pawn for just 1 tempo. How come? What am I missing? 

Thanks! 

About 3 pounds (oh wait, wrong joke).

a free pawn is almost always worth the effort imo, only when there are more pressing matters or a plan that will not work if I take it.
Sometimes a free pawn can wait, it all depends on the most forcing lines. 
I find it difficult to believe a pawn is worth 3 tempi, or the game would be a passive one where moves are quite useless. Even then, how can a pawn cost 3 tempi.
I tend to get caught up in my original plans, so mostly the free pawn can wait. 
So my guess would be a free pawn if there is no plan, is always good (if it doesn't mess up your position or give your opponent a positional edge that can create complications).
If there however is a plan, the pawn is only worth it when it doesn't stand in the way of a plan.
Unless the plan is just to win a pawn

ah... and a bishop is worth 42/70 of a Rook. and a rook is 390/702 of a Queen.

Is there a way for the OP to delete irrelevant comments?

I don't think so, but you can ask a mod

3 tempi is the usual figure quoted. In other words, if your opponent offers you a pawn you should probably capture it (1 tempo lost) even if the capturing piece will be attacked and has to move back (2 tempi lost), as long as your opponent has no other positional or initiative compensation.

I've seen grandmasters say that all other things being equal, 2 tempi are insufficient compensation for the loss of a pawn.

When you see higher rated players giving up a pawn for 1 tempo, they are probably gaining in ways you're not aware of.

No, but the people who posted the irrelevant comments can (as I have just done).

Thanks bastiann and ontomorrow. 

And yes, ontomorrow, you're right, they probably are. 

No, because then the OP would delete everything they didn't like or want to hear...which wouldn't make for much of a forum.

A pawn is worth nothing if you are getting checkmated.

If you have to give up your queen to defend a pawn, it's probably not a good idea.

lol...yes, beware of these facile guidelines, because that's all they are (at best).  Like you say, strong players disregard them all the time.  The 3 tempi=pawn thing is relatively reliable, as such things go...but the only way to get a better grasp of such matters is (I'm afraid) to actually become a strong player.

It's the same way with that 10000-hour business which (I noticed) you mentioned on your home page.  Don't get too stuck on these arbitrary numbers and assessments that people come up with...the truth is always (quite) a bit more complicated than that.

It all depends on the position

AndyC..., I'm fully aware that the 10,000 Hour Rule is a gross oversimplification. Some made it to master level in about 3,000 hours (in one study), others spend more than 20,000 hours (in the same study) to reach the same level.

There's a pawn-shop next door. I'll let you know...

Haha! 

a pawn is worth one pawn.

For information on this, I suggest looking at some high level Benko 5...bxa6 variations.