Make approximate measurements in an image, using an object with known size for scale. Online, without upload, simple and free. For the best accuracy, the objects should be close to each other — unlike in the sample image below. Read the how-to or just give it a try:
- Set the scale by drawing the first line (click and drag, drag endpoints to adjust)
- Enter the known dimension
- Draw more lines to measure other parts of the image
Known dimension: CTRLESCDEL
How to measure something in a photo
It's simple to determine distances on maps or technical drawings such as architectural (floor) plans when you have its scale and a ruler.
Because everything is in a single plane, measurements can be taken directly. The real-world dimensions are then obtained by simply applying the scale.
Photos on the other hand are a two-dimensional projection (image) of the three-dimensional world (object).
As a result, objects appear smaller with increasing distance — that's called perspective.
Without additional information, it cannot be determined whether it is a small object nearby or a large one far away (depth perception is more difficult with one eye closed).
Consequently, to determine the size of an object from a single image, a reference object for scale needs to be in the same image plane, i.e. close-by and at the same distance from the camera.
Additionally, camera lenses cause distortions (think fish-eye view).
As a result, expect this method to be useful only for estimates. The accuracy depends very much on the image.
So please don't blame me if e.g. your kitchen furniture don't fit - No Warranty
- or drag&drop an image anywhere onto this page. The picture will be scaled to fit the page width.
- Expand the editor area for a larger view
- Rotate the image as needed (Limitation: measurement lines can't be rotated with the image)
- Create the reference dimension (red) by click-and-dragging the first measurement line onto an object with known size.
- Enter the real-world length of the first dimension as reference - the other measurements will be scaled accordingly.
- Create measurement lines (green) by click-and-dragging (remove them by clicking on the 'remove' link in the measurement table below).
- Save the annotated image and the measurement data via the respective buttons or right-click the image and "Save Image As ..."
(Bug: Saved with the current resolution, not the original. Working on it.. )
Further tips for using the tool:
- Drag an endpoint to adjust a line
- Hit (or click) DEL to remove the last measurement
- Use the measurements table to remove any measurement
- Press (or click) ESC to abort drawing the current line or clear all measurements. Hit it twice within 1 second to clear the image.
- Hold (or click to toggle) CTRL while dragging to "snap" horizontal/vertical lines
- You can enter a unit in the scale, it'll show up in the results (it does not affect the measurements).
- Leave the scale empty if you want to measure pixels (pixel measurements will be off for scaled images).
Accurate measuring tools
If you need more accuracy, get out the old tape measure or calipers.
Or get a new measuring tool from Amazon* (links open in new tab) — the laser measures make quick work of it:
- Laser distance measure* (can't recommend ultrasonic ones; they sometimes have a built-in laser pointer)
- Tape measure*
- Folding ruler*