Accurate measurements are the fastest way to an accurate door quote. With a tape measure, a level and a phone camera, you can capture everything a door company needs in a single visit to each opening — and avoid a second site visit or a door that doesn’t fit.
Key takeaways
- Measure the opening, not the old door. Record width first, then height.
- Headroom, side room and backroom decide which door types and track options will fit.
- Note the jamb material, whether the floor and header are level, and what power is at the door.
- Take photos. They answer questions measurements can’t.
What you’ll need
- A 25-foot or longer tape measure (a laser measure helps for high ceilings)
- A 4-foot level
- A ladder
- Your phone, for photos
- The checklist at the end of this post
Step 1: Measure the opening width and height
Measure the finished opening — wall to wall and floor to header — not the existing door, which usually overlaps the opening.
- Width: measure between the jambs at the top, middle and bottom. Record the narrowest.
- Height: measure from the floor to the underside of the header at the left, center and right. Record all three if they differ.
Convention is width first, then height: a “12 x 14” door is 12 feet wide and 14 feet high (Janus International).
Step 2: Measure headroom
Headroom is “the distance from the header to the ceiling or any obstruction above the header” (Clopay). Measure to the lowest thing in the way — a beam, pipe, duct, light fixture, sprinkler line or unit heater.
Headroom decides more than anything else which door will fit:
- A rolling door needs room above the opening for its coil and hood. The requirement grows with door height and weight. For one rolling door model, the manufacturer lists roughly 19″ to 20½” depending on opening height (Janus Model 1950) — heavier commercial doors need more.
- A sectional door needs room for its track. One manufacturer lists about 12″ for a standard-lift door up to 12′ high with 2″ hardware, with low-headroom track options needing less and high-lift options needing more (Garaga).
These figures vary by manufacturer, model and hardware, so don’t rule a door out yourself — record what you have and let the door company check it.
Step 3: Measure side room
Side room is the wall space beside the opening that the door’s guides, brackets and operator need. Clopay measures it “from the edge of the opening (including any guide setback) to the outside of mechanisms” (Clopay). Since you don’t have the new door yet, measure what’s available instead: from each edge of the opening to the nearest obstruction (a wall, column, pipe or conduit), left and right separately. Required side room varies by operation type, and the drive side usually needs more than the other side (Janus Model 1950).
Step 4: Measure backroom (depth)
Backroom is the depth inside the building that the door and opener need — Clopay measures it from the wall to “the outermost portion of the operator” (Clopay). Measure the clear distance from the wall back to the first obstruction. It matters most for sectional doors, which travel back under the ceiling when open, and for trolley-type openers. Note anything in that path: racking, cranes, lights, sprinklers or mezzanines.
Step 5: Check the jambs and header
- Jamb material: steel, masonry (block, brick, concrete) or wood. Each uses different fasteners (Janus Model 650 installation guide).
- Condition: look for cracks, rot, rust or damage from vehicle impact.
- Plumb and flush: hold the level against each jamb. Installers check that jambs are plumb and that the guide mounting surface is flush (Janus Model 650 installation guide).
Step 6: Check the floor
Lay the level across the opening. If the floor slopes or dips, note by how much. An uneven floor can leave gaps under the door; options like a sloping bottom bar, which we offer for uneven ground on our roll-up doors, can solve it.
Step 7: Note power and controls
If the door will be motorized, note what power is available near the opening: single-phase or three-phase, and the voltage if you know it. Our openers run on single-phase (115, 208 or 230V) or three-phase (208, 230 or 460V), and high-speed doors such as our 997 and 998/999 run on three-phase power. Also note where you’d want push buttons, card readers or keypads.
Step 8: Take photos
Take at least four:
- The full opening from inside
- The full opening from outside
- The header and ceiling above the opening, showing obstructions
- Each jamb, close up
A photo with the tape measure visible is even better.
Step 9: Write down how the door will be used
- How many times a day it opens and closes
- Whether the space is heated, cooled or refrigerated
- Security needs after hours
- Whether people also walk through (a pass door may help)
- Any fire rating required by your plans or inspector
This information drives the spring cycle rating, insulation and options — see what drives the cost of a commercial door project.
Printable measurement checklist
| Item | Measurement / note |
|---|---|
| Opening width (narrowest of top / middle / bottom) | |
| Opening height (left / center / right) | |
| Headroom (header to lowest obstruction) | |
| Side room — left | |
| Side room — right | |
| Backroom (wall to nearest obstruction inside) | |
| Jamb material (steel / masonry / wood) | |
| Jambs plumb? Damage? | |
| Floor level across opening? | |
| Obstructions above or behind (pipes, lights, sprinklers, heaters) | |
| Power at door (single / three-phase, voltage) | |
| Cycles per day | |
| Heated / cooled / refrigerated? | |
| Fire rating required? | |
| Existing door to remove? |
Send it to us
Send us your measurements and photos and we’ll recommend door options. Architects and contractors can upload plans and requirements (up to five files), or contact us — we serve the five boroughs, Long Island, Westchester and Rockland.
Common questions
Should I measure the old door or the opening?
The opening. Existing doors usually overlap the opening, and their size may not match what a new door needs.
What if I don’t have enough headroom?
Tell us the number. Low-headroom track options exist for sectional doors, and a different door type may fit where another can’t.
Do I need exact measurements for a quote?
Close measurements and good photos are enough to start the conversation and narrow down options. Final dimensions should always be verified on site before a door is ordered.
