Floor plan measurement tool

How the numbers are produced

This is the checking desk. It opens on the same Elm Cottage as the home page: known wall 2.00 m, living room 3.00 m², kitchen 1.80 m², total 4.80 m², nine leaders. The work here is what happens after the first trace: move a corner, undo it, add a calibration that does not agree, and see that page 2 of a PDF does not inherit page 1.

Living room corner index 2 is the point (500, 400), the third vertex, counting from zero. Choose Living room, choose corner 3 in the list (the value is 2), set y to 300, and apply. The corner moves to (500, 300). The living room area falls from 3.00 m² to 2.50 m². The kitchen stays 1.80 m², so the total falls from 4.80 m² to 4.30 m². Undo puts the corner back to y 400, the living room back to 3.00 m², and the total back to 4.80 m². Redo walks forward again. The stack stores the plan in memory only. Refreshing throws the stack away with the plan.

Changing the vertex list does not retarget the corner until you apply. The x and y fields follow the corner you select, so a stale x from corner 0 is not written onto corner 2. If you apply a y of 300 while x still reads 500, only that corner moves. An outline that crosses itself hides the area and says the outline crosses itself. Two corners typed into the outline field, such as 100,100 500,100, are refused with a message that asks for at least 3 corners. The living room stays 3.00 m² because the bad outline is not stored.

A second calibration is how you catch a bad first length. The sample already holds 400 pixels equal to 2.00 m along y = 80. Add a line from (100, 100) to (500, 100), also 400 pixels, and type 3.00 m. The mean scale is the average of 2/400 and 3/400, which is 0.00625 metres per pixel. The original reference, still 400 pixels, reads 2.50 m. The total area reads 7.50 m². The warning says the lines do not agree. The average is what the sheet uses until you replace the segments with a single known wall or pick 1:50, 1:100, or 1:48. Those ratio buttons clear the segments and remeasure the reference line.

Open elm-cottage-2page.pdf and the page control shows 2. Select page 1, set (100, 80) to (500, 80) as 2.00 m, then select page 2. Page 2 has no calibration. The wall reads Not to scale, the warning talks about drawing units only, and the sheet length stays 400 px because the coordinate fields are still filled. Select page 1 again and the 2.00 m calibration is back. The warning hides. Page 2 did not copy page 1, and page 1 did not forget its own scale. That lasts until you refresh. Nothing is written to disk between the two pages.

Zoom is for review, not for measurement. One step in takes the view from 100 percent to 200 percent. The label reads 200%. The transform sits inside a clipped frame, so the page does not grow sideways and the pixel length of a wall does not change. You can also drag the sheet. The crosshair reads the pointer in sheet pixels, including the margin where the leaders sit. Use it to see whether a corner you typed is the corner you meant. On a phone the same zoom buttons are in the sheet bar. Pinch and drag do not recalibrate.

Where these figures get used

A reviewer marking up a trace can move one corner, read the new area, and undo if the corner was the wrong vertex. The worked move, y 400 to y 300 on living room corner 2, is a 0.50 m² change on this sample, from 3.00 m² to 2.50 m², and the total moves from 4.80 m² to 4.30 m². That is small enough to miss if you only glance at the drawing and large enough to matter on a flooring order.

A set of scans where two dimensions disagree by more than 5 percent should stay on this desk until you decide which length to keep. The 2.00 m line and the 3.00 m line on equal 400 pixel spans are the worked warning: reference 2.50 m, total 7.50 m², and the words “do not agree”. Do not export a takeoff from that average unless you know why the two dimensions differ.

Multi-page PDFs are the usual place a scale gets copied by mistake. Check page 2 after you set page 1. If page 2 still says Not to scale, that is the tool doing what the floor plan dimensions note describes: a leader is only as good as the scale on that sheet. The dimensions page shows the 1:48 versus 1:50 gap on 40 mm of paper, 1.92 m against 2.00 m.

Offset leaders, the 40 mm scale table, and the 1.92 m versus 2.00 m gap are drawn on the floor plan dimensions page.

Common questions

The rest of the desk

Each of these opens the same measuring rules on a different job. Calibration is shared. A scale you set on one page is not stored for the next visit.

• Floor plan scale calculator
• Measure floor plan
• Floor plan square footage calculator
• Room area calculator
• Floor plan takeoff