Header Size Calculator
Calculate header size for window and door openings - by span and load type, to IRC tables.
The header size calculator returns the right header lumber for any door or window opening per IRC R602.7 prescriptive tables. A header is the horizontal beam above an opening that carries the load above (roof, ceiling, upper floors) and transfers it down to the king studs and jack studs on each side of the opening. Non-load-bearing partitions need only the smallest headers (often just 2x4 flat). Load-bearing walls with rooms or roof above need larger doubled lumber: 2x8 to 2x12 depending on opening width and number of floors above. For very wide openings or any non-standard situation, prescriptive tables fall short and you need an engineered beam (LVL, glulam or steel) sized by a structural engineer.
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Frequently asked questions
Non-load-bearing wall: two 2x6. Load-bearing with just roof and ceiling above: two 2x6. Load-bearing with one floor + roof above: two 2x8. Load-bearing with two floors + roof above: two 2x10. Most exterior walls in a 2-story house need two 2x10 headers above 4 ft openings. Always check IRC R602.7 with your local amendments.
Generally 1 jack stud (trimmer) per side for headers under 6 ft, and 2 jack studs per side for headers 6-10 ft. The jack stud bears the load from the header down to the bottom plate. Wider openings or heavier loads (2 floors above) may require triple jack studs - consult the IRC table or get an engineer's review for unusual loads.
King studs run full height from bottom plate to top plate on each side of the opening - they tie the opening to the wall framing. Jack studs (also called trimmers) run from the bottom plate up to the underside of the header on each side - they carry the header's load down to the floor. Together they form the structural opening. Cripples run from the top of the header up to the top plate, completing the framing.
Yes - LVL (laminated veneer lumber), glulam (glued laminated timber) and PSL (parallel strand lumber) are stronger than dimensional 2x and allow much wider openings without sagging. A single 1.75 in x 9.25 in LVL has similar capacity to a doubled 2x12. Engineered beams are required for openings wider than IRC prescriptive tables cover (typically over 8-10 ft) and for any beam carrying unusual loads.
Non-load-bearing interior partitions technically do not need a structural header - some builders skip them and frame the opening with cripples and a flat 2x4 (called a top plate or sill, not a header). However, most jurisdictions require some kind of header even on non-bearing walls for door openings, both for stiffness and to provide a nailing surface for the door casing. Check local code.