Visit USCIS form I-864P for information on income vis a vis household size. Also read instructions on USCIS form I-864 where it is well explained as to the ratio between the income and assets, which in its simplified version means $5 in savings for each $1 in earnings.
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If you are a US citizen and you are sponsoring your spouse, you will need to have assets that are 3 (three) times the difference between your income and the poverty guideline. Read the instructions on form I-864 and also read I-864P which lists the poverty guidelines.