Can you dilute peroxide?

H₂O₂ is water soluble, so I'd say: Yep.
I'm pretty sure it's even ok to dilute it with something like shampoo or conditioner, so the mixed dye isn't too runny and is a bit more nourishing for the hair. The ratio depends, however, on the concentration you have and the concentration you want. I think it's a bit easier to work with the % values instead of the Vol, but that might be just me. 😀 (Math and Hamsta... Enemies for a lifetime!)

The values are:
40 Vol - 12%
30 Vol - 9%
20 Vol - 6%
13 Vol - 4%
10 Vol - 3%

So dilute
... a 40 Vol developer...
- 3:1 for 30 Vol (9%)
- 1:1 for 20 Vol (6%)
- 1:2 for 13 Vol (4%)
- 1:3 for 10 Vol (3%)

... 30 Vol...
- 2:1 for 20 Vol
- 1:1.25 for 13 Vol
- 1:2 for 10 Vol

... 20 Vol...
- 2:1 for 13 Vol
- 1:1 for 10 Vol

... 13 Vol...
- 3:1 for 10 Vol

(First number is the developer, second number is the water... or whatever you want to use...  ;))

Thanks very useful,Ive got a 40% wich will be ok for my bleach bath,but can dilute in future for doing roots.hamsta and math seem good friends not enemies  ;D

i always dilute my 40vol with water. OH has been doing that for nearly as long as i've been alive =)

I just had an exam on this subject...and ive forgot it ALREADY xD

haaaaaaaaaaaaaaaaaaa

-likes pippas comment-

Thanks very useful,Ive got a 40% wich will be ok for my bleach bath,but can dilute in future for doing roots.hamsta and math seem good friends not enemies  ;D

You're welcome...
But, err... just ask my sadis....pardon! poor math teacher. She's probably still traumatised from my tests.  😮 😛
(And thank god you didn't see me messing around with the calculator for my previous post 😀 😀 :D)

So basically it would work out cheaper to buy 40% and dilute?

errrr.....i guess technically it would, but i dunno if it's worth the expense. cos with 30, you know your getting 30. but with diluting 40, which doesn't take much water really, i don't think you'd be saving enough for it to be financially worth it. plus atleast you defo's know that your getting 30 with 30