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Which measurements should I always take with a tape measure, even after scanning?

Eight measurements no scan is the right tool for — and together they take under ten minutes to take yourself.

The rule behind the list

A LiDAR scan of a home is good for giving an overview, areas, and a basis for quotes. It isn't the right tool when a single measurement has to hold to the millimetre because something is going to be cut to it. That's true for professional surveys too — a surveyor or an architect also re-measures the critical dimension on site before anything is ordered.

The test is simple: is someone going to saw, drill, or order something to this number? Then take it yourself with a tape measure. If the number is being used to calculate materials, plan, or compare rooms, the scan can carry it.

The eight measurements

1. Openings something has to fit into precisely

The gap between two cabinets where the dishwasher will go. The niche for the fridge. The opening between two walls where a cabinet is going to be built. Measure the width in three places — top, middle and bottom — and use the smallest figure. Walls are rarely perfectly parallel, and it's the narrowest point that decides whether the item will actually go in.

Example: 604, 601 and 606 mm. Design for 601 mm, and order a 600 mm appliance — not the other way round.

2. Reveal measurements on doors

If you're ordering a new door, or need to know whether the sofa will fit through, it isn't the frame's outer dimensions that count, it's the reveal: the clear opening between the inner sides of the frame, and from floor to head. Measure with the door open, and measure the width at the bottom, in the middle, and at the top.

3. Niche depths

The recess behind a radiator, the bricked-up doorway, the cavity under a window. Niches often disappear in a scan because they're small or partly hidden. Three figures per niche: width, height, depth.

4. Chimney breast width and depth

A chimney breast is typically 30-60 cm in each direction and is easily read by a scan as a piece of furniture. Two figures, thirty seconds — and they're decisive for both the floor and wall areas of that room.

5. Ceiling height at a clear corner

Measure vertically from the finished floor to the ceiling, in a corner with no furniture in the way. If the ceiling slopes, measure both at the knee wall and at the ridge. Ceiling height is used for wall areas, and an error of 5 cm in the height is 5 cm around the entire perimeter of the room — in a room with an 18-metre wall perimeter that's nearly 1 m² of paint.

6. Step height and stair width

Stairs are the one stretch of a home where a scan has the hardest time keeping its bearings. Measure the stair's clear width and the height of one step, and count the number of steps. Step height times number of steps gives you the storey height — one of the most useful control figures in a multi-storey house.

Example: 17 steps at 18.5 cm = 314.5 cm from finished floor to finished floor. If the scan says 305 cm, you know the storeys are sitting slightly too close together in the model.

7. Window reveal depth

The distance from the wall surface in to the glass. In an old brick house it might be 30-40 cm; in a newer house, 10-15 cm. One figure per outer-wall type is enough — not per window. It's used for window reveals that need painting, and to know how deep a windowsill can be.

8. One long control measurement

The most important one of all, and the one people skip. Pick the home's longest unbroken wall, measure it wall to wall with a tape measure, and compare it with the scan. One figure tells you whether you can trust the rest.

Example: the tape measure says 612 cm, the scan says 617 cm. The difference is 5 cm, that is 5 ÷ 612 × 100 = 0.8%. You can apply that percentage across the whole home — and for areas the error is roughly double, because an area is two lengths multiplied together.

How to take them correctly

• Measure above the skirting, not at it. Skirting is typically 1-2 cm thick and runs down both sides — measure against the skirting and the room comes out 2-4 cm too narrow.
• Always measure in three places for a figure that has to hold: near each end and in the middle. If the numbers differ, the walls aren't parallel — and then you need to know both the smallest and the largest.
• Write it in centimetres or millimetres, never as "about four and a half metres". Also note where you measured.
• Hold the tape measure level. A tape that sags gives too large a figure. Over 4-5 metres this is a real source of error when measuring alone.
• Measure in the same spot every time, if you'll need to compare later — otherwise you're comparing two different points on a wall that isn't straight.

The measurements you can safely leave to the scan

The list above is deliberately short. The scan can handle everything else, and there's no reason to reach for a tape measure for it:

• Room areas for overview, comparison and material calculations.
• Wall areas for painting — there's wastage and a couple of coats to allow for anyway.
• How the rooms sit relative to each other and the home's layout.
• Roughly where furniture will fit and passage widths.
• Where windows and doors sit within the walls.

That's exactly the division of labour that makes a scan worth doing: it takes the ninety percent of measurements that are tedious to take yourself, and you take the ten that have to hold.

What HouseSense does

HouseSense works in internal measurements — wall surface to wall surface — so every figure in the app is the same kind of measurement you take yourself with a tape measure. That's the precondition for the list above making any sense at all: you can only check an app if it measures at the same point you do.

The app doesn't claim a centimetre precision it can't back up. The principle is that the drawing may be dressed up; the numbers may not. So the eight measurements above aren't an admission that the scan is poor — they're the honest division of labour between a tool that measures fast, and a tape measure that measures one spot correctly.

You can also draw the home like graph paper and enter your own tape-measure readings in whole centimetres. If you've taken the eight measurements anyway, you already have everything you need.