Need help calculating Child Support in California

I have been divorced for 6 years, and when I got divorced because of the situation I was in and wanting to be out of the marriage I waived spousal support, and he agreed to cover child care and some schooling but beyond that we didn't have anything else in writing.
In the last couple years we have come to an agreement mutually together that he would pay a certain amount regarding Child Support but every year he wants to re-negotiate and I am getting sick of this because it becomes very abusive and I get so stressed about how much yelling he will do and the derogatory text and emails I get because he doesn't want to pay support anymore.
I live in California, and my daughter is 7 yrs old.
We have a 50/50 split on custody.

Is there a calculator online that I can use to help get me a number on what it roughly should be?

Also I have recently gotten married again, and so has my ex. He is telling me that my new husbands annual income factors into how much child support he should have to pay towards his own daughter. Is this correct? He is also saying that because he has since had acouple more kids that his child support should decrease because of the new kids in his new marriage.

Any help would be great.