I have never used grams in anything (except grahams as in crackers!
). I use ounces because that is what I am used to. I have made eighty-three 36 bar batches of soap to date (122 ounces of oils, plus water & lye). One batch was crumbles and lye heavy for no apparent reason. one batch I grabbed a bottle of canola/olive blend which looked exactly like my olive oil bottle and so it did not work out. One batch came up oozing oil and big holes and I don't know why, but I rebatched it and it was fine.
Out of 83 batches, I've never used anything but ounces. I did realize that I have to be careful because my digital scale does its thing in the format of pounds:ounces:10th ounces. When weighing, if you want 19 ounces, you want 1:03:00 (16 ounces = 1 pound).
I absolutely would not worry about using ounces for the liquid; however WEIGH them on the scale. Do not go by a measuring cup. Not all measuring cups measure the same.
Happy Soaping!