How to measure a door opening correctly
Measuring is where a mistake is the most expensive to fix: a slab made to the wrong size can't be returned or reworked. Measuring isn't hard. You need a metal tape measure (a soft tailor's tape sags and adds error), a pencil, paper and a level or a level app on your phone. It takes about twenty minutes per apartment. If the opening is tall, measure with two people.
The main rule: not one point, but three
Walls are rarely even: an opening might be 800 mm at the bottom and 815 mm at the top. Measure each dimension at three points and take the smallest.
Step 1. Width
Between the left and right jambs: at the bottom (about 20 cm from the floor), mid-height, and at the top (20 cm from the lintel). Example: 812, 806, 819. Working width 806 mm.
Step 2. Height
From the floor to the top lintel at three points: near the left jamb, in the middle, near the right jamb. Measure from the finished floor. If the laminate or tile isn't laid yet, add the whole future floor build-up: screed, underlay, the finish itself. The gap between "measured off the concrete" and "floor's laid" can easily reach 5–8 cm. If the floor isn't in yet, write down the height off the concrete and the planned floor build-up separately.
Step 3. Wall thickness
The depth of the opening from one wall face to the other, at two or three spots. This number decides whether you need a jamb extension (a board that adds to the frame's depth). A telescopic frame comes in 80, 100 and 120 mm, and if the wall is thicker, an extension of 100, 150 or 200 mm is added. It's the item most often "forgotten" in a preliminary quote, only to show up on the invoice later.
Step 4. Geometry
Hold a level against both jambs. If they're out of plumb, tell your manager: a telescopic frame may work better, it forgives unevenness, while a flush frame needs a perfectly flat wall. Also check the lintel: if it sags or slopes, mention that too.
How to write down the result
For each opening:
- ✓Room: bedroom
- ✓Width: 812 / 806 / 819 → working 806
- ✓Height: 2035 / 2030 / 2038 → working 2030, floor already finished
- ✓Wall thickness: 175 mm
- ✓Jambs: even
- ✓Opens: into the room, handle on the right
That last line matters as much as the numbers: which side the door opens is set at the factory and can't be changed after production.
Opening size ≠ door size
A slab is always smaller than the opening: a gap stays between the frame and the wall for expanding foam and leveling. How much depends on the frame type, wall thickness and how even your opening is, so don't convert your measurements into a door size yourself. Send your manager the numbers you recorded. We'll size the door — that's our job and our responsibility. If you've already calculated it yourself, send that too: two numbers side by side beat one.
Sizes with no surcharge
Width 400–900 mm, height 1800–2100 mm in 50 mm steps: no surcharge within that range, and 850 mm costs the same as 800. Wider and taller (950–1000 mm, 2150–2300 mm) are made to order, +20% on the slab price. Timeline: 30 days from deposit for a standard size, 45 days for a custom one.
Special cases
- ✓An opening wider than a meter: can't be covered by one slab. Send us the sizes and we'll find an option.
- ✓Sliding doors: separately measure the free wall to the side, where the slab slides to. It must be at least as wide as the slab, with no outlets, switches or radiators.
- ✓An arched opening: a frame is rectangular, so an arch is either boxed in or left without a door. Decide before the finishing work.
- ✓An opening you're still planning to change: widen or wall it up first, then measure.
What to do next
Walk through your apartment with a tape measure, record every opening using the scheme above, and send it to us: you'll get a line-item quote within the day.