Construction glossary · Wood framing
What is Jack stud (trimmer) in 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.
Updated June 2026 · Reviewed by the Ruh construction team
Jack studs support header, set inside kings
Estimating wood framing scope this week? Watch Ruh take off a real plan in 30 minutes.
Book a walkthroughA 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.
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
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.
Try Ruh on a real bid. 100% money-back guarantee if you are not satisfied.*
*Scoped delivery, terms apply. Read the guarantee terms
How Ruh handles Jack stud (trimmer)
Ruh reads the framing plan and door and window schedule, finds each opening, and pulls the header size and jack count called out at each end. It computes jack length from the wall stud height minus header depth and bottom plate, tallies jacks by length into the stud count, and prices them on your own price book stud line. The estimator reviews the jack counts against the header schedule and signs off.
See framing estimating softwareJack 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.
Still measuring by hand? Your next takeoff can run while you review this one.
See it on your plansRelated terms
Keep going: read the full guide or explore framing estimating software.
See Ruh price a bid from your own drawings.
AI takeoff and estimating on your price book, your estimator signs off.
Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.