Internal door measurements

I’ve encountered this with older door frames. Where customers wanted to avoid the cost of replacing the frames or ordering bespoke doors, I have, at their request, trimmed suitable solid-core doors beyond the manufacturer’s stated allowance. In those cases, sufficient timber remained to achieve a secure fit and a good finish. However, exceeding the trimming allowance can compromise the door’s construction, and any certified fire resistance can no longer be relied upon. Each door and frame needs assessing individually before proceeding.

If the door is of "hollow" construction you usually have approx 20mm timber at bottom. ( do not trim top),so trimming 13mm off bottom should leave approx 7mm.But ensure blade in circular saw is sharper to avoid chipping.
I also recommend taking door before cutting this again will reduce chance of chipping.

You’re not missing something – this is a very common UK problem, especially in older houses. You basically have three realistic options, and only one of them involves “off-the-shelf” doors.
Why you’re stuck with 1981 mm doors
Modern standard internal doors are:
1981 × 762 / 686 / 838 mm
Designed around modern ceiling heights and frames
Most hollow-core doors only allow 10–15 mm trim per edge (sometimes less)
Trying to take 40–50 mm off a standard hollow door will destroy
: Buy solid core / solid timber doors and cut them down
Best long-term solution
Look for:
Solid core (engineered)
Or solid pine / oak
These can usually be trimmed:
Up to 30–40 mm per edge
Sometimes more depending on construction

Thanks for your message.
You’re right — standard internal doors today are usually 1981mm high (6'6"), so your existing door frames are slightly shorter. Trimming that much off a modern hollow-core door would weaken it, so it’s not recommended.

You have a few good options:

Order made-to-measure doors – many suppliers can custom-size doors down to your exact height.

Use solid-core doors – some can be trimmed more (up to 25–30mm from each end).

Reduce the height of the frame opening by adjusting the head casing or fitting a threshold strip (less ideal but sometimes practical).

I’d be happy to measure up and recommend the best approach depending on your door type, style, and budget.

Order a bespoke door or use a slightly taller door with a modified frame

You can order custom made doors or I could cut door and replace framework of door or I could lower door frame or buy solid doors

the best option would be find the closest size up from the door you require and trim down the top and hinge side of the door to fit.

Hi to your questions. The top and bottom of the door can be trimmed down. It is the width mainly that becomes difficult to trim, as there is a tolerance in the glued battens inside the door itself on the sides/width.
As long as the shape for both themTop and bottom rail is kept relatively the same visually the door can be trimmed down.
We use a circular and a plane. Very simple

Get plain doors and trim to height and re install the wood bar over hole

Trim of top and bottom or you would need to get door blank and make door to size

You can trim the door at the bottom and rebuild it. The bottom can be cut and then some board applied back with pins.

Custom-Made Doors – Some suppliers offer bespoke sizes, though they can be pricier. Try checking with specialist joinery companies or trade suppliers.

Rebate the Frame – If there’s a bit of room, you could slightly raise the head of the door frame to accommodate a standard 1981mm door.

Reduce the Door Height with a Lipping Replacement – If the doors you’re looking at have solid lippings (thicker timber edges), you can remove the original ones, cut the door down further, and fit new lippings to retain strength.

Rehang Existing Doors – If your current doors are still in good condition, you might consider sanding, repainting, or refinishing them instead of replacing.

Check Salvage Yards – Architectural salvage yards sometimes have older-sized doors that might fit.

Have them bespoke made

You would have to read the manufacturers guide with the door which tells you how much can be trimmed off. If it was a fire door definetly not but it could be done door would just need re lipping afterwards so it was back to a solid core

You can bottom off and reset the bottom rail inside the door with glue and clamps . Once dry you can hang the door