Measuring & Planning

How to Measure for a Custom Steel Door

Our crew takes the final measurements on every door we build, so you are never on the hook for a wrong number. These instructions are for the earlier stage: when you need a rough size for a quote, when a builder is framing a new opening, or when you want to check that a replacement will fit before you call us.

1. Measure the existing door

Width. Measure edge to edge at the top, middle and bottom. Use the smallest figure.
Height. Measure from the top edge to the bottom edge on the left and right sides. Use the smallest figure.
Thickness. Most steel entry doors are 1 3/4 inches thick, but confirm it. Thickness affects the lockset and hinges.
Jamb depth. Measure the frame from the interior wall face to the exterior wall face. This tells us how the new frame will sit in the wall.

2. Check the frame

Frame width and height. Measure inside edge to inside edge at three points across and two points up. Record the smallest of each.
Squareness. Measure both diagonals corner to corner. If they differ by more than about 1/4 inch, the opening is out of square and will need correcting before a steel frame goes in.
Plumb and level. Put a four-foot level on both jambs and on the sill. Note which way anything leans and by how much.

3. Record the hardware

Hinges. Note the height from the bottom of the door to the center of each hinge, and the hinge size.
Lockset. Measure the backset, which is the distance from the door edge to the center of the lock. The common sizes are 2 3/8 and 2 3/4 inches. Note the lock height from the floor.
Swing. Stand outside facing the door. If the hinges are on your right and the door opens away from you, it is a right-hand inswing. Write it down exactly that way.

4. The things people forget

Floor clearance. Measure the gap under the door, and note whether the finished floor inside is higher or lower than outside.
Threshold and weatherstrip. Note what is there now. New doors usually come with their own.
Obstructions. Light fixtures, downspouts, steps, railings and anything the door or a sidelite could hit when it swings.
Photos. One straight-on shot from inside, one from outside, and one of each jamb edge. Photos answer half of our follow-up questions.

Measure twice, in inches, to the nearest 1/16. Write every figure down as you take it. If two measurements disagree, take a third rather than guessing which one was right.

Rough opening vs. door frame size: what is the difference?

The frame size is the outside dimension of the steel frame we build. The rough opening is the hole in the wall it goes into, which has to be slightly larger so the frame can be shimmed plumb and square. The door size is smaller again, because it sits inside the frame.

For most of our doors the rough opening runs about half an inch wider and taller than the frame. The exact figure is printed on the shop drawings for your door, and those drawings are what a framer should build to. If you give us a rough opening that already exists, we size the frame to it, so tell us which number you are giving us.

How to check an opening for level, plumb and square

Level means the sill is flat side to side. Plumb means the jambs are perfectly vertical, both left to right and front to back. Square means every corner is a true 90 degrees.

Lay a four-foot level across the sill. Note the gap under either end.
Hold the level against each jamb on the face and on the edge. A jamb can be vertical in one direction and leaning in the other.
Measure the two diagonals. Equal diagonals mean a square opening.
Sight along the wall from the side to check it is not bowed.

A steel frame is rigid. It will not bend to follow a crooked opening the way a wood frame can be persuaded to, so anything more than about 1/4 inch out should be fixed in the framing before we arrive.

Common measuring mistakes when ordering a custom steel door

Measuring the old door slab and calling it the opening size.
Measuring at one point only. Openings are rarely the same width at the top and the bottom.
Forgetting the finished floor. A tile floor going in later can take 3/4 inch off the height you have.
Mixing up handing. Always describe it from the outside.
Not telling us about stucco, stone or brick returns that wrap into the opening.
Leaving out jamb depth, which decides whether the frame needs extensions to meet the interior trim.

Measuring for double doors, sidelites and transoms

Measure the whole opening as one unit, not each piece. For a pair of doors we need the total width and height, and whether both leaves need to operate or one can be fixed most of the time. For sidelites and transoms, give us the full opening and tell us the door width you want. We work out the sidelite and transom sizes from there, because the mullions between them take up room that is easy to miss. See the double doors, sidelite doors and transom doors pages for configurations.

Preparing the opening and the house before delivery

Most installation problems are opening problems. The door itself is finished and checked before it leaves the shop, so what decides how install day goes is the hole it is going into. Here is what we need to see when we arrive.

Framed to the drawings. Rough opening at the size shown, with solid blocking or doubled studs on both sides and a straight header. In masonry, the opening cut clean with no loose material.
Plumb, level and square within 1/4 inch. We can shim out small variance. We cannot shim out a bowed header.
Sill ready. Flat, solid, and sloped or pan-flashed so water goes out, not in. The finished exterior grade should sit below the threshold.
Weather barrier in place. House wrap or flashing membrane lapped into the opening so we can tie the frame flashing into it.

Clear access. A path wide enough for several people carrying a unit that can weigh hundreds of pounds, with no wet concrete or fresh landscaping in the way.
Power on site for drills and, for masonry, a hammer drill.
Interior finishes protected. Flooring covered, nearby furniture moved.
Someone to make decisions. Handle height, threshold detail and trim questions come up on the day, and we need an answer from the owner or builder.

The project readiness checklist covers all of this in a form you can print and walk the site with.

Did not find what you needed?

Ask us directly. We would rather answer a question before an order than fix a problem after one.

Call (512) 773-4192 Get a Free Quote Read the FAQ