Check out the uscis federal poverty guide.
For the 48 Contiguous States, the District of Columbia, Puerto Rico, the U.S. Virgin Islands, Guam, and the Commonwealth of the Northern Mariana Islands:
Household Size
Fee Waiver (Form I-912)
150% of HHS Poverty Guidelines*
Reduced Fee for Form N-400
400% of HHS Poverty Guidelines*
1
$22,590
$60,240
2
$30,660
$81,760
3
$38,730
$103,280
4
$46,800
$124,800
5
$54,870
$146,320
6
$62,940
$167,840
7
$71,010
$189,360
8
$79,080
$210,880
Add $8,070 for each additional person
Add $21,520 for each additional person