How much maple syrup so I use to prime my keg?

New to the whole kegging thing. Force carbonated my last batch.

Everything I've read says to use half the amount of corn sugar when priming a keg as compared to bottling. My latest batch is for a maple wheat ale that calls for a mix of corn sugar and maple syrup for priming. I know sugar contents are different in all these fermentables (DME takes more for priming etc.)

How do I determine how much sugar/syrup to prime with? Is it as simple as cutting the amount in half or should I be looking at gravities of each substance? Would a program like BeerSmith help or is it overkill for a somewhat beginning extract brewer like myself?

Thanks!

There are two issues here: 1) how much sugar do you need to prime a keg, and 2) how much sugar is in maple syrup.

Most people report using about half as much sugar as normal to naturally prime a keg, though I suspect that this is somewhat variable. You can work out the numbers using Boyle's law, etc., but it would get complicated. Mostly, just try it and see if you like the level of carbonation. Half as much as normal seems like a good starting place.

As for maple syrup, you can dilute some in water to determine it's sugar concentration using a hydrometer. You might also want to do a fast fermentation test to see how much of the sugar is fermentable, but I suspect that most of it is. This thread has some tips.