To calculate header size:
Determine the measurement of your doorway's rough opening. Say 50 inches.
Divide that measurement by 12:
50 inches / 12 =4.1667 inches.
Round up to the nearest even whole value to find the door header height.
4.1667 inches →6 inches.
Combine this value with the wall frame material thickness, typically 4 inches, to get a lumber size of 4" × 6".
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