# Gel and western blot lane labeller

> Label gel and western blot lanes online: split lanes, add angled or straight labels and a PageRuler, Precision Plus or GeneRuler marker. PNG or SVG.

URL: https://www.labcanvas.com/tools/gel-lane-labeler

Open a gel or blot image, set the number of lanes and the tool splits the image into equal lanes (centres at x₀ + (i + ½) × lane width), which you then drag onto the real lanes. Type a label for each lane, horizontal or angled above it, and add a molecular-weight marker column: pick PageRuler Plus, PageRuler, Precision Plus Protein, GeneRuler 1 kb or NEB 100 bp (band sizes as the manufacturers list them) and drag each mark onto its band, or type your own sizes and positions. Rotate to straighten a tilted gel, crop, and download a PNG or an SVG whose labels stay editable text. The image stays in your browser.

## Quick answer

- **What it does:** Adds lane labels (horizontal or angled) and a molecular-weight marker column to a gel or western blot image, with lanes split evenly and adjustable, and exports PNG or SVG.
- **Formula:** lane centre xᵢ = x₀ + (i + ½)(x₁ − x₀)/n;  first ladder guess y = y_top + (ln M_top − ln M)/(ln M_top − ln M_bottom) × (y_bottom − y_top)
- **Example:** 8 lanes across x = 50–850 px are 100 px wide with centres at 100, 200 … 800 px; with PageRuler Plus from 250 kDa at y = 60 to 10 kDa at y = 470, the 55 kDa mark starts at y = 252.9 px.

Free, in the browser, no account needed. Updated 2026-10-19.

## Features

- Lanes split evenly (1–60), then each lane centre dragged onto its lane
- A label per lane, horizontal, 30°, 45°, 60° or vertical, above the lanes
- Marker column on the left or right from PageRuler Plus, PageRuler, Precision Plus Protein, GeneRuler 1 kb or NEB 100 bp, with sizes checked against the manufacturers’ pages
- Custom ladders: sizes with their y positions in pixels, or spaced on a log scale
- Rotate by any angle (or 90° steps) to straighten a gel, and crop each side
- PNG (DPI kept) or SVG with editable text; opens TIFF (8 or 16 bit) as well as PNG and JPEG

## How to use it

1. **Open and straighten**: Drop the gel or blot image (PNG, JPEG or TIFF). Rotate it a few degrees if the lanes are tilted, and crop the edges.
2. **Lanes and labels**: Set the number of lanes, drag the green markers onto the lane centres, and type each lane’s label; choose the label angle.
3. **Marker and export**: Pick the ladder you ran (or type sizes), drag each orange mark onto its band in the marker lane, then download PNG or SVG.

## At a glance

| | |
| --- | --- |
| Lanes | 1–60, split evenly, then dragged |
| Labels | Above the lanes, 0°, 30°, 45°, 60° or 90° |
| Ladders | PageRuler Plus, PageRuler, Precision Plus Protein Dual Color, GeneRuler 1 kb, NEB 100 bp, or custom |
| Image | PNG, JPEG, WebP or TIFF; rotate and crop |
| Output | PNG (DPI kept) or SVG with editable text |

## How it works

$$\text{lane width} = (x_1 - x_0) / n$$

$$\begin{aligned} &\text{centre of lane } i\ (i = 0 \ldots n - 1) \\ &\quad = x_0 + (i + \tfrac{1}{2}) \times \text{lane width} \end{aligned}$$

$$\begin{aligned} &\text{first guess for ladder band } M: \\ &y = y_\mathrm{top} + \frac{\ln M_\mathrm{top} - \ln M}{\ln M_\mathrm{top} - \ln M_\mathrm{bottom}} \\ &\qquad \times (y_\mathrm{bottom} - y_\mathrm{top}) \end{aligned}$$

$$\begin{aligned} &\text{height an angled label needs} \\ &\quad = \text{text width} \times \sin\theta + \text{font size} \times \cos\theta \end{aligned}$$

**Lanes.** Wells are cast at equal spacing, so the lanes start evenly divided over the area the current lanes cover (the whole width for a new image); drag each green marker onto the middle of its lane where a gel ran unevenly or was cut. The labels are centred on, or for angled labels start at, the lane centres, above the image.

**The marker column.** In SDS-PAGE the logarithm of a protein’s molecular weight falls about linearly with the distance it migrates, which Weber and Osborn established with 40 proteins of known size (Weber & Osborn 1969); DNA fragments in agarose behave similarly over the middle of a gel’s range. The tool uses this only for a first guess: the top and bottom band of the chosen ladder go near the top and bottom of the image and the bands between are spaced on that log scale. Then drag each orange mark onto the real band in the marker lane, because gradient gels, prestained proteins and the ends of the range depart from the straight line. To read the size of an unknown band from the ladder, use the [western blot molecular weight calculator](https://www.labcanvas.com/tools/western-blot-mw-calculator). Prestained ladders such as PageRuler give approximate sizes: the manufacturer notes that their apparent molecular weight varies with the gel and buffer system and from lot to lot.

| Ladder | Unit | Bands, top to bottom |
| --- | --- | --- |
| PageRuler Plus Prestained | kDa | 250, 130, 100, 70, 55, 35, 25, 15, 10 |
| PageRuler Prestained | kDa | 180, 130, 100, 70, 55, 40, 35, 25, 15, 10 |
| Precision Plus Protein Dual Color | kDa | 250, 150, 100, 75, 50, 37, 25, 20, 15, 10 |
| GeneRuler 1 kb DNA Ladder | bp | 10000, 8000, 6000, 5000, 4000, 3500, 3000, 2500, 2000, 1500, 1000, 750, 500, 250 |
| 100 bp DNA Ladder | bp | 1517, 1200, 1000, 900, 800, 700, 600, 500/517, 400, 300, 200, 100 |

**Rotating and cropping.** Rotation turns the image about its centre into a canvas just large enough to hold it (width \(W\cos\theta + H\sin\theta\), height \(W\sin\theta + H\cos\theta\)), with the corners filled white or black, and then the crop removes the number of pixels you set from each side. Rotation by angles other than 90° resamples the image. Image-integrity guidance accepts straightening, cropping and labelling, but adjustments must be applied to the whole image, and blots should not be cut and spliced without marking the joins (Rossner & Yamada 2004); keep the unprocessed original.

**Output.** The PNG has the image at its own pixel size with margins added for the labels and marker column, and keeps the DPI the original file recorded. The SVG embeds the processed image and writes labels, marks and unit as text in Arial, so they can be edited in Illustrator, Inkscape or the LabCanvas figure editor.

Sources: Weber K, Osborn M. The reliability of molecular weight determinations by dodecyl sulfate-polyacrylamide gel electrophoresis. *J Biol Chem* 1969;244:4406–4412, [doi:10.1016/S0021-9258(18)94333-4](https://doi.org/10.1016/S0021-9258(18)94333-4). Rossner M, Yamada KM. What’s in a picture? The temptation of image manipulation. *J Cell Biol* 2004;166:11–15, [doi:10.1083/jcb.200406019](https://doi.org/10.1083/jcb.200406019). Ladder sizes: the manufacturers’ product pages linked in the table.

## Worked example: an 8-lane western blot with a PageRuler Plus marker

A western blot image 900 × 520 pixels: the ladder in lane 1, then a control, two siRNAs and a time course (0, 2, 6 and 24 h). The lanes run from \(x = 50\) to \(x = 850\).

- **Lanes.** 8 lanes over 800 pixels are 100 pixels wide; their centres are at \(50 + (i + \tfrac{1}{2}) \times 100\) \(= 100, 200, 300 \ldots 800\) pixels.
- **Labels.** Type M, Ctrl, siRNA 1, siRNA 2, 0 h, 2 h, 6 h, 24 h and choose 45°: each label starts at its lane centre and rises to the right, and the figure gains just enough space above the blot for the longest one.
- **Marker.** Choose PageRuler Plus Prestained. With its 250 kDa band at \(y = 60\) and its 10 kDa band at \(y = 470\), the bands between are spaced as below: 55 kDa at \(60 + (\ln 250 - \ln 55)\) \(\div\, (\ln 250 - \ln 10) \times 410 = 252.9\) pixels. On the example blot these sit exactly on the bands; on a real gel, drag each mark onto its band.
- **Export.** Download the PNG for a slide or the SVG to keep the labels editable in a figure.

| Band (kDa) | \(y\) (px from the top) |
| --- | --- |
| 250 | 60.0 |
| 130 | 143.3 |
| 100 | 176.7 |
| 70 | 222.1 |
| 55 | 252.9 |
| 35 | 310.4 |
| 25 | 353.3 |
| 15 | 418.4 |
| 10 | 470.0 |

For a DNA gel, GeneRuler 1 kb from 10 000 bp at the top to 250 bp at the bottom works the same way; its brighter reference bands at 6000, 3000 and 1000 bp help you match the marks to the right bands.

## Questions

### How do I label lanes on a western blot?

Put a short label above each lane (sample, treatment or time), centred on the lane, and the marker sizes with tick marks beside the ladder lane. In this tool: open the image, set the number of lanes, drag the lane markers onto the lanes, type the labels and choose a ladder; then download PNG or SVG.

### How do I add molecular weight markers to a blot image?

Choose the ladder you ran (for example PageRuler Plus: 250, 130, 100, 70, 55, 35, 25, 15, 10 kDa) and drag each mark onto its band in the marker lane, or type your own sizes with the y position of each band. The sizes are written beside the image with tick marks.

### Should lane labels be angled?

Use horizontal labels when they are short (1–4 characters) and fit over the lane; angle them at 45° when they are longer than the lane is wide, so they do not overlap. Keep all labels in one figure at the same angle and size.

### What are the band sizes of the PageRuler Plus and Precision Plus ladders?

PageRuler Plus Prestained: 250, 130, 100, 70, 55, 35, 25, 15 and 10 kDa. PageRuler Prestained: 180, 130, 100, 70, 55, 40, 35, 25, 15 and 10 kDa. Precision Plus Protein Dual Color: 250, 150, 100, 75, 50, 37, 25, 20, 15 and 10 kDa.

### How do I straighten a tilted gel image?

Rotate it by the tilt angle, usually 1–3°: positive turns clockwise. Then crop away the filled corners. Rotation applies to the whole image, which image-integrity guidelines accept, but keep the original file.

### Can I edit the labels afterwards?

Download the SVG: the labels, marker sizes and ticks are text and lines over the embedded image, so they can be edited in Illustrator, Inkscape or the LabCanvas figure editor.

### How do I find the molecular weight of my band?

Use the ladder: log(MW) is about linear in migration distance. The western blot molecular weight calculator fits that line to the ladder bands you click and reads off your bands’ sizes.