depends on how much co2 is already in the beer . I like mine carbed lightly . 1/2 ounce to the gallon is light . 1 ounce is going to be heavy if you have plenty of co2 already in it .
For a brown I say 1.5 to 2.0 volumes per liter . so if your beer is 70 degrees then you have approximately 1.0 volumes of co2 in it already . 68 degrees about .9 volumes .
I t takes 4 grams of sugar to make 1 volume of co2 in 1 liter of beer.
6 gallons I will just call 23.0 liters . actually 22.7..
Priming sugar = volumes to add ( you have 1.0 and want 1.5 you need .50 ) X 4 (grams of sugar ) X volume of beer ( 23 liters ) .
.50 X 4 = 2.0 X 23 liters = 46 grams of sugar about 1.6 ounces I think , to add in to make 1.5 volumes of co2 which is good for a nut brown . Browns should be lightly carbed according to my expert brown ale taste buds .
1 ounce ( by volume not weight in a measuring cup ) table sugar weighs 32 grams
1 TBSP weighs 14.5 grams
1 TSP weighs 4.75 grams
If you add 1.5 to 2.0 ounces by volume or weight you should get a nice beer . I used to use 5/8 cup or 1 ounce to gallon and always came out over carbed after a while in the bottle . 5 oz in my opinion is way over carbed for any dark beer.