When using US 4 needles the gauge is 6 sts per inch and 8 rows per inch.

When using US 7 needles the gauge is 4.5 to 5 sts per inch.

Also, FYI when decreasing for the top of the hat, you will need to switch from the circular needles to DPNS as the circumference gets smaller.

This hat will fit my 22.5 inch circumference head.

The mittens will fit my 7.5 inch circumference hands.

Of course, both will stretch to fit head/hands slightly larger.

Adjust accordingly by adding stitches or using larger needles if you need something larger.