How to Extract Data from a Plot or Graph Image
Have you ever found a chart in a paper, report, or textbook and needed the actual numbers behind it? This guide shows you how to extract data from any plot image using PlotExtract — a free, browser-based tool that requires no installation or account.
What you need
- The image of the plot (JPEG, PNG, or any common format)
- A browser (Chrome, Firefox, Edge, or Safari)
- PlotExtract — free, no sign-up
Step 1: Open your image
Go to plotextract.com/app and load your chart image in one of three ways:
- Drag and drop the image file onto the canvas
- Click Open image and select the file
- Paste from clipboard with Ctrl+V (or Cmd+V on Mac)
The image will appear in the main canvas ready for calibration.
Step 2: Calibrate the axes
Calibration tells PlotExtract what coordinate values correspond to pixel positions on your axes. You need to set two reference points on each axis.
Calibrate the X axis:
- Click the X1 calibration button in the left panel
- Click on a known point along the X axis (for example, where X = 0)
- Type the value (0) in the box that appears
- Repeat for X2 using a different known X value (for example, X = 10)
Calibrate the Y axis the same way using two known Y values.
Tip: Choose calibration points that are as far apart as possible for the most accurate results. Use axis tick marks where you know the exact value.
PlotExtract supports both linear and logarithmic axes. Use the scale selector in the calibration panel if your axis is logarithmic.
Step 3: Click your data points
With calibration complete, switch to the Data tool and start clicking on data points in your chart.
- Each click places a marker and records the real-world coordinates
- The X and Y values appear in the data table on the right
- You can move a point by dragging it, or delete it with right-click
For scatter plots, click each individual point. For line charts, click as many points as you need to reconstruct the curve accurately.
Step 4: Add more series (optional)
If your chart contains multiple data series (multiple lines or groups of points), click + Add series in the series panel. Give each series a name and colour, then click its data points separately.
Step 5: Export to CSV
When you have captured all the data you need:
- Click the Export button in the right panel
- Choose to export the active series or all series combined
- A CSV file downloads immediately — open it in Excel, import into Python with
pandas, or use it in R
Tips for better accuracy
- Zoom in using the scroll wheel to place points more precisely on small features
- Hold Shift while clicking calibration points to snap to perfectly horizontal or vertical lines
- Use Ctrl+Z to undo any mis-clicked point (up to 50 steps)
- For noisy data, clicking the trend rather than every individual point often gives cleaner results
Frequently asked questions
Does PlotExtract work offline? Yes. Once the page has loaded, PlotExtract runs entirely in your browser. Your image is never uploaded anywhere.
What if my chart axes don't start at zero? That's fine — just enter the actual values at your calibration points. PlotExtract doesn't require zero to be visible.
Can I digitize a bar chart? Yes. Click the top of each bar. The Y coordinate gives you the bar's value, and you can use the X coordinate or just rename series to label each bar.