Welcome to the forum!
I do the same as TAKeyser, I'll split packets for 1-gal batches (it'll last quite a while in the fridge) but I use a whole packet for a 3 gallon batch.
For all the rest of the ingredients, just keep the same proportions: either multiply by 3 for a 1-gal recipe or multiply by 3/5 if it's a 5 gallon recipe.
"The main ingredient needed is 'time' followed closely by 'patience'." - The Bishop 2013
"Good grief! If someone wanted to murder you, all they would have to do is ship you a 55 gallon barrel of honey and watch you document working yourself to death!" - Vance G
"When you consider that laziness and procrastination are the fundamentals of great mead, it is a miracle that the mazer cup happens." Medsen Fey, 2014
"Sure it can be done. I've never heard of it, but I do things I've never heard if all the time. That is the beauty of being a brewer!" - Loveofrose, 2014