Retirement tax questions

For RMD, should we Use Box 1 even if there is an amount in Box 2a (Taxable Amt) that's lower??

Or does it not matter???

Thanks again

 

On my husbands 1099-R for his pension:

Box 1 Gross Distribution = $40279.46

Box 2a Taxable Amt   =   $40201.58

Box 4 Federal Tax  =  $4020.18

Box 5 Employee Contribution = $77.88

Box 7  =   "7"I

IRA/SEP/SIMPLE Box   =  Empty (Unchecked)