Dumb ass only tells you how to dilute 16oz to 1% in a big batch. If you have 3% peroxide and want a shot glass of 1% which is about 30ml then just add 20ml water to 10ml of 3% and you got an oz of 1%.
Same formula as he used but using the final volume as your V2.
3% x Xml = 1% x 30ml
3X = 30
X = 30/3
X = 10ml of your 3%
I use 35% food grade peroxide and we keep a 500ml bottle of 3% by the utility sink for first aid, dripping on my toothbrush after use etc so to fill that bottle with 3%:
35% x Xml = 3% x 500ml
35X = 1500
X = 1500/35
X = 42.86ml
Easy enough to make just want you need. Peroxide starts breaking down faster the more dilute it is so the 3% you buy at the drug store has preservatives in it but the 35% food grade doesn't. Health food or hydro stores usually have it. Shipping is a problem as it is considered hazardous goods and the 35% or higher certainly is.