What’s the right way to think about how much to give to charity?

I’d like to hear from peo­ple about a pro­cess they use to de­cide how much to give to char­ity. Per­son­ally, I have very high in­come, and while we donate sig­nifi­cant money in ab­solute terms, in rel­a­tive terms the amount is <1% of our post-tax in­come. It seems to me that it’s too lit­tle, but I have no moral in­tu­ition as to what the right amount is.

I have a good in­tu­ition on how to al­lo­cate the money, so that’s not a prob­lem.

Back­ground: I have a wife and two kids, one with sig­nifi­cant health is­sues (i.e. med­i­cal bills—pos­si­bly for life), most money we spend goes to pri­vate school tu­ition x 2, the above men­tioned med­i­cal bills, mort­gage, and mis­cel­la­neous life ex­penses. And we max out re­tire­ment sav­ings.

If you have some sort of quan­ti­ta­tive sys­tem where you figure out how much to spend on char­ity, please share. If you just use vague feel­ings, and you think there can be no rea­son­able quan­ti­ta­tive sys­tem, please tell me that as well.

Up­date: as sug­gested in the com­ments, I’ll make it more ex­plicit: please also share how you de­ter­mine how much to give.