Further to a reading a similar thread dealing with visa extensions requirements (retirement):
and a link provided by Pragmatic:
The same company provides a similar page when the extension is based on being A Member Of A Thai Family, which one assumes is up to date:
Extension based on marriage - thailawonline
Which is well worth a read for anyone who is applying on that basis.
Plenty of info tips, procedures, required "paper work" and the usual suggestion of visiting your designated TIO for any clarifications.
There is also a copy the Thai Ministry regulation/police order number.
THE REGULATION
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Police order 777/2551
2.18 In the case of a family member of a Thai (applicable only to parents, spouse, child, adopted child or child of his/her spouse):
Permission will be granted for a period of not more than 1 year at a time.
(1) The alien has obtained a temporary visa (NON-IM)
(2) Proof of family relationship
(3) In the case of a spouse, the marital relationship shall be dejure (legitimate) and de facto;
(4) In the case of a child, adopted child or child of his/her spouse, the said person must not be married, must be living with the family, and must be less than 20 years of age; or
(5) In the case of a parent, one of parents must have an average annual income of not less than 40,000 baht per month or a money deposit of not less than 400,000 baht for expenses within a year.
(6) In case of marriage with a Thai lady, the husband who is an alien must have an average annual income of not less than 40,000 baht per month or a money deposit in a local Thai bank of not less than 400,000 baht for the past 2 months for expenses within a year.
(the paragraph about “husband” should be considered as “husband” or “wife”.)