Heatmap Builder
Visualise matrix data as colour-coded heatmaps. Choose from 5 colour scales and export as PNG or PDF.
The Heatmap Builder turns a grid of numbers into a colour-coded visualisation, mapping low-to-high values onto a smooth gradient so patterns, hotspots, and outliers jump out at a glance — all rendered live on a canvas in your browser.
A heatmap is one of the clearest ways to read two-dimensional data: each cell is shaded by its value relative to the rest of the dataset, so dense activity and quiet gaps become obvious without squinting at a table of figures. Set the number of rows and columns, label each axis, and either type values directly into the editable grid or paste a range straight from Excel or Google Sheets. Choose from five colour scales — Hot, Cool, Green, Plasma, and Greyscale — and the gradient automatically anchors your dataset's minimum and maximum to the two ends of the scale, with a matching legend showing the exact range. You can toggle the in-cell value labels on or off and pick a small, medium, or large cell size to suit the density of your data. People use it to:
- Visualise website traffic or activity by day of week and hour of day
- Spot trends and anomalies across a correlation matrix or score table
- Map scheduling, attendance, or capacity intensity across two dimensions
- Turn a spreadsheet range into a shareable PNG or printable PDF for a report
Everything runs locally — the grid is drawn entirely on a canvas in your browser, so nothing you type is uploaded and your data never leaves your device. There is no account, no sign-up, and no limit on how many heatmaps you build, making it safe for sensitive figures and quick enough for a throwaway sketch.
- Set the number of rows and columns, then enter the row and column labels (one per line).
- Click Generate Grid to build the editable table with sample values you can replace.
- Type values into the cells, or paste a range copied from Excel or Google Sheets — the heatmap updates instantly.
- Pick a colour scale, toggle in-cell values, and choose a cell size; the legend shows your min and max.
- Export the finished heatmap as a PNG image or a printable PDF.
Hot, Cool, Green, Plasma and Greyscale. The scale automatically maps your dataset's min/max to the two ends of the gradient.
Yes — copy any cell range from Excel or Sheets and paste into the grid. Tab-separated rows are detected automatically.
Nowhere. The heatmap is rendered on a canvas in your browser and nothing is uploaded.
A heatmap shades each cell of a grid by its value, so colour stands in for magnitude. Brighter or more saturated cells mean higher values and cooler or paler cells mean lower ones, which makes hotspots, gaps, and patterns across two dimensions instantly visible.
Pick the scale that best fits your data and audience. Hot, Cool, and Green give an intuitive low-to-high feel, Plasma offers high contrast for fine detail, and Greyscale suits print or colour-blind-friendly output. Every scale anchors your dataset's minimum and maximum to its two ends automatically.
Yes. Click Download PNG to save the rendered canvas as an image, or PDF to open a printable page with your title and heatmap that you can save or print. Both use the heatmap exactly as shown, including labels and the active colour scale.
Use the legend below the heatmap: it shows the colour gradient alongside the minimum and maximum values in your data. A cell's colour tells you where its value sits between those two extremes, and you can switch on in-cell labels to read the exact number too.