It's so close it makes little difference.
1 fluid ounce.
They weigh about 1 ounce !
1 ounce
1.22 oz or 34.38 g - one tbsp (US) weighs 0.61 oz or 17.19g
1 ounce
1/16 of an ounce
1 ounce or 28.3 grams
1 pounds = 16 ounce
1 ounce
A quart of blackberries weighs 1 to 1 1/2 pounds.
Ounces are a unit of weight, so yes, 1 ounce of anything = 1 ounce of anything else.