How to measure a room for a floor plan

Cover: AI-generated editorial illustration. The measurement diagram below is an original, dimensioned example, not a survey of a real home.

A room can be 4.2 metres wide and still leave less than 4.2 metres for furniture. A radiator projects from one wall. A door needs space to open. A window starts halfway along the wall where you hoped to put a tall cabinet.

A useful floor plan records those interruptions as well as the outline. Here is a practical way to collect the measurements, check the arithmetic and carry the notes into a room planner.

Make one set of room notes

Start with paper, a pencil and a tape or laser measure you know how to use. Sketch the room from above, give each wall a letter and write one unit at the top of the sheet. Record wall lengths, ceiling height, door and window locations, opening directions and fixed objects such as radiators. Add photos with matching wall letters. These are the kinds of information covered in IKEA's room-measuring guide.

Keep the original readings. If you record 4200 mm, enter 420 cm when a planner asks for centimetres, or 4.2 m when it asks for metres. Do not enter 4200 into either of those fields. In feet and inches, 10 feet 6 inches is 10.5 feet, not 10.6 feet.

Put uncertain readings in a separate list. “Behind radiator: not measured” is more useful than a plausible number that looks confirmed a week later.

Choose the surfaces you are measuring between

For the furniture layout in this guide, overall dimensions run between the finished inside wall faces. That is different from an outside building dimension or the distance between wall centre lines.

Write that convention beside the drawing. Also note anything that projects beyond those faces: skirting, trim, a hearth or a radiator. A cabinet against the skirting may have a different usable gap from a picture hung higher on the same wall.

In your planner, check what the selected wall dimension represents before treating it as clear room width. Adding wall thickness to a drawing does not turn an inside measurement into a centre-line measurement automatically. Use a distance check between the same two surfaces you measured on site.

A worked room: 4200 × 3600 mm

The original example below is deliberately simple. Its inside rectangle is 4200 mm wide and 3600 mm deep. Wall A contains a window. Wall B has a radiator. Wall C has a door.

Original vector illustration by Renovaitor. The 1500 mm dimension covers the window frame zone; it is not a clear opening measurement. Open the full-size diagram to inspect the labels.

Measure Wall A end to end, then record its parts using consistent endpoints:

• Inside corner to the near outside edge of the window frame: 700 mm.
• Outside edge to outside edge of the window frame: 1500 mm.
• Far outside edge of the frame to the next inside corner: 2000 mm.
• Full wall: 4200 mm.

The check is 700 + 1500 + 2000 = 4200 mm.

If your partial readings total 4180 mm but your overall reading is 4200 mm, there is a 20 mm disagreement. Do not distribute that difference across the drawing to make it close. Recheck the endpoints and the measurements. You may have mixed a frame edge with the clear opening, or included a small return in only one reading.

This arithmetic checks that the notes agree. It does not prove the tape was straight or that the wall is square.

Separate the opening from its frame

A “900 mm door” note is ambiguous. It might describe a leaf, a framed zone or the space available to pass through. Label what you measured and record the other dimensions when they matter to the decision. For windows, also record sill height and any opening movement that could meet nearby furniture. IKEA's measurement guidance distinguishes room, window, frame and door details.

In our example, a note for Wall C could read 350 mm to the frame + 900 mm frame zone + 2950 mm to the corner = 4200 mm. That locates the framed zone. It does not promise a 900 mm clear passage or establish that a boxed sofa can turn through it. The door symbol in the diagram only shows the opening direction.

Record projections before placing furniture

Our example radiator projects 180 mm into the room. From the opposite inside wall face to the radiator face, the remaining distance is 4200 − 180 = 4020 mm.

A furniture layout that uses all 4200 mm across that part of the room would overlap the radiator by 180 mm. This is why a clean rectangle alone can give a misleading impression of fit.

The 4020 mm is a geometric measurement, not permission to place furniture against a heat source. Required operating and safety clearances depend on the actual appliance and its instructions. Record those separately instead of guessing a universal gap.

Similarly, the rectangle's 4.2 × 3.6 = 15.12 m² area does not tell you which furniture arrangement works. The door, projections and routes through the room still matter.

Check the drawing against a second measurement

Before arranging furniture, compare another known distance with the drawing. Calibrating an imported image using one length establishes scale along that reference; it cannot prove the rest of a distorted photograph is accurate.

For this exact rectangular example, a corner-to-corner diagonal would be approximately 5.53 m, calculated from the 4.2 m and 3.6 m sides. That is a property of the example, not a target to force onto your home. If the real outline or readings disagree, preserve that uncertainty and remeasure instead of assuming every corner is a right angle.

Take the notes into Renovaitor

Open the free room planner and replace its starting dimensions with your own. The current starter uses centimetres or inches. For the example above, choose Centimeters, enter 420 for width and 360 for depth: the preview shows 4.2 m × 3.6 m, with area rounded to 15.1 m². This was checked in the live planner. The starter saves on the current device; follow the sign-in prompts when continuing work into your account.

Place openings and furniture using your notes. Keep height, fixed-projection and appliance-clearance notes alongside the drawing: the starter's window fit check does not assess window height, and a visual symbol cannot replace those checks.

Use the sofa-fit layout walkthrough to compare arrangements after you have the room notes. Once the layout is plausible, an AI keep/change/avoid brief can help you explore the look. Manual planning starts free; AI generations use credits and their images do not verify dimensions.

Before relying on the plan, check that you have:

• The measurement date, units and inside-face convention.
• Every wall segment, with openings and their offsets.
• Clearly distinguished frame, leaf and clear-opening dimensions where needed.
• Fixed projections, heights and opening directions.
• A second distance check and a visible list of anything still uncertain.

These are furniture-planning notes. Construction, fitted installations and formal property measurements require the appropriate professional checks.