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Construction glossary · Wood framing

What is a jack studin construction?

A jack stud, also called a trimmer, is a shortened wall stud that runs from the bottom plate up to the underside of a header and carries the header's load down to the floor. It is nailed to the full-height king stud beside it. Jack studs are what actually hold up everything bearing on the opening, so their count and length matter on every door and window.

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Updated August 2026 · Reviewed by the Ruh construction team

Aka TrimmerSupports Header weightDoubled if Span over 6 ftHeight Sets header level
The definition

Jack stud (trimmer), explained.

A jack stud (trimmer) is the load-bearing member of an opening's framing in light-frame wood construction. It sits inside the king stud, runs from the bottom plate to the bottom of the header, and transfers the header reaction straight to the plate and floor below. The header sets on top of the jacks, so jack length equals rough opening height. King studs run full height past the header to tie the opening into the wall and resist racking, while jacks do the vertical carrying. Wider openings and bigger tributary loads call for doubled or tripled jacks at each end, which the framing plan or a beam schedule will specify. In a typical 8 ft wall the jack length is the rough opening height, often around 82 in to 83 in for a standard door once you account for the bottom plate and header depth. Jack studs are usually the same stock as the wall studs, 2x4 or 2x6, and they get face-nailed to the king stud per the nailing schedule.

How it is measured

Jack studs are counted per opening and measured by length, both read off the framing plan and the door and window schedule. Count the jacks called out at each side of every rough opening, usually one per side for narrow openings and two or three per side for wide headers or heavy loads. Jack length equals the rough opening height, which you get by subtracting the header depth and the bottom plate thickness from the wall stud height, or by reading the rough opening height in the schedule. Tally jacks by length so cut lists group cleanly. Jacks are pulled from the same 2x4 or 2x6 wall-stud stock, so they roll into the overall stud count on the plan's wall framing notes.

Worked example

Jack stud length: worked example for an 8 ft wall

Worked example

Take a 8 ft (96 in) wall with a header over a window opening. Wall stud height is 92.625 in (a precut stud), the bottom plate is 1.5 in, and the doubled 2x10 header is 9.25 in deep. Jack length = stud height minus header depth = 92.625 - 9.25 = 83.375 in. The plan calls for one jack per side, so 2 jacks at 83.375 in = 166.75 in total, or 13.9 lf. If the opening is wide enough that the schedule calls for two jacks per side, that is 4 jacks at 83.375 in = 333.5 in = 27.8 lf. Buying 92.625 in precut studs, each jack uses one stud with 9.25 in of drop left over, so 2 jacks = 2 studs and 4 jacks = 4 studs. Always confirm jack count against the header schedule before cutting.

How Ruh handles it

How Ruh handles Jack stud (trimmer).

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Jack stud (trimmer): frequently asked questions

What is the difference between a jack stud and a king stud?+

The jack (trimmer) is the short stud that runs to the bottom of the header and carries its load to the floor. The king stud runs full height alongside the jack, ties the opening into the wall, and resists racking. Every opening needs both.

How many jack studs do I need under a header?+

One per side handles most narrow openings. Wide headers or heavy tributary loads call for two or three jacks per side. The framing plan or header schedule specifies the count, so follow it rather than defaulting to one.

How long is a jack stud?+

Jack length equals the rough opening height, which is the wall stud height minus the header depth and bottom plate. For a 8 ft wall with a 9.25 in header and a 92.625 in precut stud, the jack is about 83.4 in.

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Related terms

King studCripple studStudBottom plate (sole plate)HeaderHurricane tie

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