How much powdered sugar should be used ...

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... to replace granulated sugar in a bread recipe?

Is there a general rule for this type of substitution? By volume? By weight?

Would the proportion depend on the type of bread?

Unfortunately, I only have powdered sugar end brown sugar readily available.

Thanks!

For a bread recipe, you could probably get away with a simplified substitution of using an amount of powdered sugar equal in weight to the amount of granulated sugar.  Powdered sugar takes up a much higher volume than granulated, so  substituting by volume is trickier.  

If you want to be exact, powdered sugar is 3% cornstarch by weight, so you would increase the weight slightly to account for that.