How to measure the opening for a new front door

To measure a front door opening, measure the width at three heights (bottom, middle and top) and the height at three points (left, centre and right), take the smallest figure for each, check the opening is square by measuring both diagonals, and note the internal and external floor levels. Add the opening direction and a photo and you have everything needed for a quote. The final manufacturing size should always be confirmed by the fabricator or installer who will fit the door.

What will you need?

• a steel tape measure of at least 3 metres, or a laser measure;
• a spirit level;
• pen and paper, or your phone for photos and notes;
• a second person helps with the higher measurements.

Step 1: decide what you are measuring

There are two different situations:

• Replacement with the old frame removed: measure the structural opening, wall to wall and from floor to lintel.
• New build or an opening already prepared: measure the finished opening, with plaster and finishes already on.

If you don't know whether the old frame is coming out, measure inside the existing frame and say so in your request. The fabricator will confirm.

Step 2: width at three points

Measure the width between the sides of the opening:

1. about 10 cm above the floor;
2. halfway up;
3. about 10 cm below the lintel.

Write down all three in millimetres. The usable width is the smallest.

Step 3: height at three points

Measure from the floor to the lintel:

1. next to the left-hand jamb;
2. in the centre;
3. next to the right-hand jamb.

Write down all three. The usable height is the smallest.

If the finished floor has not gone down yet, give the expected thickness of the floor finish, or measure from a datum line marked on the wall.

Step 4: square and plumb

Measure both diagonals of the opening, corner to corner. If they are the same or very nearly so, the opening is square. A big difference means the opening is out of square and the installation will need to compensate.

Hold the level against both jambs to check they are plumb, and on the threshold to check it is level. Note any deviation.

Step 5: floor and threshold

Note:

• whether the internal and external floors are at the same level;
• whether there is a step, and how high it is;
• whether the entrance is sheltered from rain by a canopy, balcony or recess.

This helps in choosing the threshold and the bottom seal.

Step 6: opening direction

Decide whether the door opens inwards or outwards. On houses, inward opening is the most common.

Then, standing on the side the door opens towards, see where the hinges are:

• hinges on the left: left-hand opening;
• hinges on the right: right-hand opening.

For a pivot door, say which side you would like the pivot axis on and how far from the edge, if you already have an idea.

Step 7: wall thickness and context

Measure the thickness of the wall at the opening and note where the insulation is, if you know. Take photos:

• straight on, from outside and inside;
• of each corner, to show the condition of the opening;
• of the whole front of the house, to put the door design in context.

Openings with side lights or a top light

Many entrances have a fixed glazed side light next to the door or a top light above it. In that case:

• measure the whole opening, including the fixed lights;
• also measure the current width of each element (door, left side light, right side light, top light);
• say whether you want to keep the current layout or redesign the entrance.

A redesigned entrance might swap a side light for a wider door leaf, or turn a hinged door into a pivot door. Those decisions change the leaf sizes, so it is worth discussing them before the quote is finalised.

What happens after you measure?

Your measurements are used for a quote and an initial check of the design. From there, the fabricator or installer who will fit the door carries out the site survey, decides the fitting tolerances, frame type and fixings, and confirms the manufacturing sizes. It is this final survey that goes into production. If the floor or plaster is not finished yet, the final survey should wait until they are, or be done against clearly marked datum lines.

What to send with your quote request

• width and height (all three measurements for each);
• diagonals;
• internal and external floor levels;
• opening direction;
• wall thickness;
• photos;
• the type of door you want: monobloc, pivot, with a flush, grooved, glazed or stainless steel panel;
• RAL colour or wood-effect finish, if you have already chosen.

Common mistakes

• Measuring only once: an opening is almost never perfect. Three measurements protect you from surprises.
• Forgetting the finished floor: a door measured before the floor finish goes down can end up too short or catch on the floor.
• Getting the opening direction wrong: describe it in words and send a photo.
• Rounding: write everything down in millimetres.

Next steps

Before you measure, you can choose the design and colour in the Portancora door visualiser, using a photo of your entrance. Once your measurements are ready, send us your request. We have been making bespoke aluminium front doors for 25 years and work with fabricators and installers who confirm the measurements and fit the door.