Guides · Floor Plan Measurement
Setting scale is the most important step in measuring a floor plan. Get it right and every polygon you trace converts to accurate square footage. Get it wrong and every measurement is off by the same proportional error. This guide shows exactly how to do it and how to verify your calibration.
When you trace a polygon the tool calculates its area in pixels. Without a scale reference, pixels have no real-world meaning. You provide the conversion by clicking two points along a wall where you know the real-world distance and entering that distance. The tool derives a pixels-per-foot ratio and applies it to all polygon areas automatically.
1. Identify a wall or dimension on the plan where you know the real-world length. 2. Zoom in to that wall so you can see the endpoints clearly. 3. Click at the start of the known segment. 4. Click at the end of the known segment. 5. Enter the real-world length and press Enter. 6. All polygon areas update instantly based on the new calibration.
Longest labeled wall on the plan (best): A 40-foot exterior wall gives maximum accuracy. Total house width or depth if labeled: Often the most reliable reference. Room dimension labels: Use the longer of the two labeled room dimensions. Scale bar: Click its endpoints and enter the length it represents. Door width (last resort): Standard doors are 2'8" (32") or 3'0" (36") — works if that's all you have, but gives less accurate calibration than longer references.
Calibration divides real-world length by pixel length. Any click error (say 3 pixels) is divided by total pixel length. For a 10-pixel reference: 3/10 = 30% error. For a 200-pixel reference: 3/200 = 1.5% error. The effect of click uncertainty drops dramatically as reference length grows.
Using the printed scale notation on a resized image: "1/4" = 1'" is only accurate at the original print size. On a digital image calibrate from known dimensions, not the printed ratio. Interior vs exterior mismatch: If a labeled dimension spans exterior-to-exterior, click the exterior wall faces. Forgetting to recalibrate after uploading a new image: Scale is image-specific. Set it fresh on each uploaded floor.
After setting scale, trace a room with a labeled size — "12 × 14" should return approximately 168 sq ft. If you get 145 or 190, recalibrate using a different (preferably longer) reference wall. A quick verification trace takes 30 seconds and gives you confidence before tracing the full floor plan.
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