Measure the opening width, height, and depth before you order

The three measurements you need are the width of the opening, the height of the opening, and the depth of the frame itself. Most people measure wrong the first time because they measure the door instead of the frame, or they measure only one spot when the frame is slightly out of square. Take all three measurements in at least two places each, write them down, and use the smallest number for width and height — that is the actual opening size.

You will also need to know whether your frame is inside-mounted (the frame sits inside the wall opening) or outside-mounted (the frame wraps around the outside of the wall). This changes what size frame you order. Most residential doors are inside-mounted, but some exterior doors and closet doors are outside-mounted.

Key Takeaways

  • Measure the width and height of the opening at the top, middle, and bottom — use the smallest number for each, because the frame may be slightly out of square.
  • Measure the depth of the existing frame (the thickness from the inside edge to the outside edge) to match it when you order.
  • Check whether your frame is inside-mounted or outside-mounted, because the two types require different measurements and different replacement frames.
  • Write down all measurements in inches and bring them with you when you shop, because frame sizes are not standard and a salesperson will need the exact numbers.

Measure the width of the opening

Close the door and look at the frame from the side. You are measuring the distance between the left jamb (the vertical piece on the left) and the right jamb (the vertical piece on the right), measured on the inside of the frame where the door closes.

Measure at three heights: near the top of the frame, in the middle, and near the bottom. Write down all three numbers. If they are different, use the smallest one — that is your true opening width. The frame may have settled slightly over time, which is normal.

If the opening is wider at the top than at the bottom, the frame is leaning inward. If it is wider at the bottom, the frame is leaning outward. Either way, use the smallest measurement, because that is where a new door will have to fit.

Measure the height of the opening

Measure the distance from the bottom of the frame (the sill, or threshold) to the top of the frame (the head jamb). Measure at three points: on the left side, in the middle, and on the right side. Write down all three numbers.

Again, use the smallest measurement. The frame may be taller on one side than the other if the house has settled. A new frame will need to fit into the smallest opening, so that is the number you use when you order.

Do not measure from the floor to the ceiling. Measure only from the bottom of the existing frame to the top of the existing frame. The frame itself is what you are replacing, so the frame dimensions are what matter.

Measure the depth of the frame

The depth is the thickness of the frame from the inside edge to the outside edge. This is the measurement most people forget, and it is the one that causes problems when the new frame arrives.

Look at the frame from the side. Place a tape measure against the inside edge of the frame (the edge closest to the room) and measure straight across to the outside edge (the edge closest to the wall). This number is usually between 4.5 and 6.5 inches for interior doors, depending on the wall thickness. For exterior doors, it is often 6 to 8 inches.

Write this number down. When you order a replacement frame, you will need to tell the supplier the depth so they send you a frame that fits the wall opening you have.

Determine whether your frame is inside-mounted or outside-mounted

An inside-mounted frame sits inside the wall opening. The edges of the frame are visible from both sides of the wall, and the frame does not wrap around the outside of the wall. Most interior doors and some exterior doors are inside-mounted.

An outside-mounted frame wraps around the outside of the wall. The frame extends beyond the wall on one or both sides, and you can see it from the outside of the house. Many exterior doors and some closet doors are outside-mounted.

Look at your door from the side. If the frame sits flush with the wall on both sides, it is inside-mounted. If the frame extends beyond the wall on one side (usually the outside of the house for exterior doors), it is outside-mounted. This matters because the two types require different measurements and different replacement frames.

Write down your measurements and check them twice

Create a straightforward list with these numbers: opening width (smallest of the three measurements), opening height (smallest of the three measurements), frame depth, and whether the frame is inside-mounted or outside-mounted. Include the door type — interior, exterior, closet — so the salesperson knows what you are replacing.

Before you leave the house, measure one more time. Measure the width and height again at a different spot to confirm your numbers are consistent. If the new measurement is different from the first one, measure a third time and use the smallest number. Ordering a frame that is too large is a common and expensive mistake.

Take a photo of the door and frame from the front and from the side. When you go to the store or call a supplier, you can show them the photo and your measurements together. This helps them confirm you measured the right thing.

Know what to do if the opening is out of square

If your three width measurements are very different from each other — for example, 32 inches at the top, 32.5 inches in the middle, and 33 inches at the bottom — the frame is out of square. This is common in older houses.

Tell the supplier that the opening is out of square and give them all three measurements. They may recommend a frame that is slightly smaller than the largest opening, so it will fit through the smallest opening. You will then need shims (thin wooden wedges) to fill the gaps between the new frame and the wall, which is a normal part of frame replacement.

Do not try to force a frame that is too large into an opening that is out of square. The frame will bind, the door will not close properly, and you will have to remove it and start over.

Frequently Asked Questions

Should I measure the door itself or the frame?

Measure the frame, not the door. The frame is what you are replacing. The door may be slightly smaller than the opening to allow for hinges and clearance, so measuring the door will give you the wrong frame size.

What if I measure and the numbers do not match the standard frame sizes at the store?

Frame sizes are not standard. Tell the supplier your exact measurements and ask whether they can order a custom frame or whether they have a stock frame close to your size. Many suppliers can order custom frames in any width and height, though it may take longer and cost more than a stock size.

Do I need to remove the old frame before I measure?

No. Measure the opening with the old frame in place. The new frame will be built to fit into the same opening, so the old frame's dimensions are what you need.

What if the frame depth is not a standard size?

Bring your depth measurement to the supplier and ask what frame depths they stock. If your wall is thicker or thinner than standard, they may be able to order a custom depth or recommend a shim kit to make up the difference.

Can I order a frame online if I have my measurements?

Yes, many suppliers accept online orders with measurements. Before you order, call or email the supplier to confirm that your measurements are correct and that they can deliver a frame in your size. Some online suppliers have a return policy if the frame does not fit, but it is better to measure carefully the first time.