Line interval, DPI & engrave time
Enter your spot size and get the line interval where scan lines just touch — in mm, DPI, LPI and lines/mm. Or check the interval you already use: see how much the lines overlap, how long the job will take, and what size to make the image.
1Your beam
2Engraving settings
How the calculator works
When a laser engraves a filled area, the head scans one line, steps sideways by the line interval, and scans the next. If the step equals the width of the spot, the lines just touch. LightBurn calls that the ideal: lines that touch without overlapping.
The time estimate counts every scan line, including both edges:
The second term is the time spent speeding up and slowing down at each end of the line, assuming the machine overscans so it reaches full speed before the design starts. It is only added if you enter an acceleration. One-way scanning is a rough estimate: we count it as twice the time, as if the return move ran at the same speed. Real machines also add small pauses between lines.
Common values
| lines/mm | Interval (mm) | DPI / LPI | lines/cm |
|---|---|---|---|
| 5 | 0.2 | 127 | 50 |
| 6 | 0.1667 | 152.4 | 60 |
| 8 | 0.125 | 203.2 | 80 |
| 10 | 0.1 | 254 | 100 |
| 12.5 | 0.08 | 317.5 | 125 |
| 15 | 0.0667 | 381 | 150 |
| 20 | 0.05 | 508 | 200 |
How to find your spot size
- Maker’s spec. Many makers publish a spot size. Some diode modules list two numbers, one per direction, because the spot is not round. Use the number at right angles to the scan direction for the interval.
- Measure a burned line (our method). What has to touch is the width of the burned line on your material at your working power and speed, which is not always the optical spot. Burn a short line with the settings you plan to use, on the material you will engrave, and measure its width with a scaled loupe or microscope.
- Run an interval test. LightBurn’s Interval Test engraves patches at different intervals. The patch where lines just touch gives you the effective line width on that material.
Spot size changes with focus. If you defocus to soften an engraving, the spot grows and a wider interval will still look solid.
Interval, darkness and time
At the same power and speed, the energy put into each square millimetre is inversely proportional to the interval:
So halving the interval doubles both the energy and the job time. If an engraving is too dark, a wider interval is often a better fix than lowering power, because it also saves time. To carry an engraving setting to a different machine, use the laser power & speed converter, which keeps this area energy the same.
Non-round spots and scan angle
If your spot is not round, the line interval is measured across the scan lines, so the ideal interval depends on which way the head scans. In LightBurn, changing the Scan Angle from 0 to 90 turns the scan from horizontal to vertical, which swaps the spot dimension that matters. Dot Width Correction shortens each scan line to make up for the beam’s width. LightBurn suggests about half the beam’s thickness, always less than the interval, and notes it varies with the material. It does not say which direction to measure; because the setting shortens lines along the scan, we use the spot size along the scan.
Image resolution
LightBurn advises preparing images at the DPI that matches your chosen interval, so that each scan line lines up with one row of pixels. The calculator shows the pixel size for your width and height.
FAQ
- What line interval should I use for laser engraving?
- Start with an interval equal to your spot size measured across the scan lines, so neighbouring lines just touch without overlapping. LightBurn describes this as the ideal and suggests testing between 120 and 300 DPI (0.08–0.2 mm). Then confirm with an Interval Test on your material.
- How do I convert lines per mm to DPI?
- DPI = 25.4 × lines per mm, and the line interval in mm is 1 ÷ lines per mm. So 10 lines/mm is 254 DPI and a 0.1 mm interval; 8 lines/mm is about 203 DPI and 0.125 mm.
- Does a smaller line interval make engraving darker?
- Yes, at the same power and speed. Halving the interval puts twice the energy into each square millimetre and roughly doubles the job time, because the head runs twice as many lines.
- What image resolution should I use for laser engraving?
- Make the image DPI match your line interval, so each scan line gets one row of pixels. At a 0.1 mm interval that is 254 DPI, or 1,000 pixels for a 100 mm wide engraving.
Sources
- LightBurn documentation, Image mode settings (DPI = 25.4 ÷ line interval, lines that just touch, Dot Width Correction about half the beam’s thickness, overscanning, scan angle).
- LightBurn documentation, Perfect image engraving (Interval Test, 120–300 DPI, image DPI matching the interval).
Last checked 2026-10-27 · Calculated values; no machine was used to make this page.