Enter the full measured kerf width and your desired finished rectangle dimensions. Both cases use the same target width and height: retaining the rectangle as an external part, or removing it to leave an internal opening. Results describe the laser centerline path, assuming a uniform cut centered on that path.
All inputs and outputs use metres (m). Divide millimetres by 1,000 before entering them: 0.20 mm = 0.00020 m; 50 mm = 0.05000 m. Multiply results by 1,000 to read them in millimetres.
Accepted input bounds are 0–0.01 m for kerf and 0.000001–10 m for each target dimension, with 0.000001 m input increments. These are calculator limits, not machine capacity specifications or claims of measurement accuracy.
An internal rectangular opening additionally requires both target dimensions to be strictly greater than the kerf. If either internal path dimension is zero or negative, that case has no valid rectangular centerline path under this model. The calculator displays the arithmetic result; it does not automatically suppress invalid geometry. External-part results remain a separate case.
Zero kerf gives zero offsets and unchanged path dimensions. Unavailable results are not zero and must not be used as dimensions.
A centered cut removes k/2 on either side of its centerline. Moving each of two opposite edges by k/2 changes the rectangle’s total width or height by k. For a retained external part, the path therefore grows; for an opening, it shrinks. The equations above are a geometric derivation under this symmetric-cut assumption.
LightBurn documents outward and inward compensation for closed shapes and the need to establish compensation experimentally. See Kerf – What It Is and How to Compensate.
The signs here mean positive outward and negative inward relative to the target rectangle. Check how your design software interprets offsets, particularly for nested shapes. Apply compensation once: use either the compensated path dimensions or the target dimensions with the appropriate offset.
| Target width × height | Full kerf | External offset per edge | External path width × height | Internal offset per edge | Internal path width × height |
|---|---|---|---|---|---|
| 50 × 30 mm | 0.20 mm | 0.10 mm outward | 50.20 × 30.20 mm | 0.10 mm inward | 49.80 × 29.80 mm |
| 20 × 10 mm | 0.30 mm | 0.15 mm outward | 20.30 × 10.30 mm | 0.15 mm inward | 19.70 × 9.70 mm |
| 50 × 30 mm | 0 mm | 0 mm | 50 × 30 mm | 0 mm | 50 × 30 mm |
| 0.20 × 10 mm | 0.20 mm | 0.10 mm outward | 0.40 × 10.20 mm | 0.10 mm inward | Invalid: calculated width is zero |
The defaults are illustrative measurements, not recommended kerf values. Use a measured kerf representative of your material and cutting setup. LightBurn’s guide describes experimental calibration and complications from irregular beam shapes. This calculator assumes one uniform kerf in both directions. Source: LightBurn kerf guide.
The model calculates straight-edge rectangular dimensions. It does not model corner radii, taper through material thickness, local kerf variation, dimensional uncertainty, or fit clearance. Matching nominal external and internal dimensions does not specify a press fit or sliding fit. Confirm the intended fit with a measured test piece.
Formula basis and further reading
Artwork creation required before publication: create and register a 400 × 400 pixel WebP thumbnail, then reference its registered asset ID in the first image block. Use the established cheerful yellow five-point star mascot with hands, floating without separate legs or feet, on a white background with playful navy, blue and teal graphics illustrating inner and outer rectangular cut paths. Inspect neighboring thumbnails before creation. No verified thumbnail asset ID was supplied, so no image reference has been invented.