What income is used to determine the Long Term Capital Gains Tax Brackets? Is it Total Income less the Capital Gain? Line 9 on the 1040 (before adding the cap gain)?

I understand the Long Term Cap Gains Tax Bracket allows for a Single Filer to have up to $40.4K in income before paying any capital gain tax, but I am confused as to what income is included when determining that Tax Bracket?  Is it lines 1 through 6b plus line 8?  That is, line 9 (Total Income) without the Cap gain amount (line 7)?