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LidarKit

Compress LAS to LAZ

Lossless compression to roughly a tenth of the size. Nothing is uploaded and nothing is discarded.

Drop your LAS or LAZ file here

or choose a file

LAS 1.0–1.4 · multi-gigabyte files welcome

No upload. Conversion runs in a Web Worker on your device — this app has no server component and no upload endpoint. How it works

What you gain, and what it costs

LAZ compression is the rare case where the tradeoff is close to one-sided. You are not choosing between size and quality — LAZ stores exactly the same data as the LAS it came from — so the only real cost is a small amount of CPU time whenever the file is read.

Typical LAS sizeExpected LAZ sizeSaved
100 MB10 – 20 MB~85%
1 GB100 – 200 MB~85%
10 GB1 – 2 GB~85%

Ranges reflect the commonly cited 7–20% figure for LASzip on real survey data. Your ratio depends on point density, how many attributes are populated, and the coordinate scale factors in the header — so treat these as an expectation, not a guarantee.

Why lossless means lossless here

LAZ does not approximate anything. It exploits the fact that neighbouring LiDAR points are highly correlated — consecutive coordinates differ by small amounts, classifications repeat, return numbers cycle — and encodes those differences with an arithmetic coder instead of storing each value in full. Decompression reverses the arithmetic exactly.

This converter verifies that claim rather than repeating it: the test suite converts LAS to LAZ and back and asserts the result isbyte-for-byte identical to the input — header, VLRs, EVLRs and every point record. How that is tested.

When to compress

  • Archiving. There is no reason to store uncompressed LAS long-term. Same data, a fraction of the disk.
  • Sending files to clients. A 12 GB LAS is awkward to transfer; a 1.4 GB LAZ usually is not.
  • Cloud storage costs. An 85% reduction applies directly to the monthly bill.
  • Not for a file you are about to read repeatedly in a tight processing loop, where the per-read decompression cost adds up. Keep a working LAS, archive the LAZ.

What is preserved

The original public header block, all user VLRs and EVLRs — including the coordinate reference system, whether stored as GeoTIFF keys or WKT — extra bytes, and every per-point attribute. The naive way to build a LAZ writer drops user VLRs and takes the CRS with them; this one does not.

Frequently asked questions

Does compressing LAS to LAZ lose any data?
No. LAZ is lossless: it re-encodes exactly the same point records, so every coordinate, classification, intensity and GPS time value comes back bit-for-bit identical when decompressed. This is different from mesh or image compression — there is no quality setting and nothing to tune, because there is nothing being discarded.
How much smaller will my file get?
Typically 10 to 20 percent of the original size, so an 80 to 90 percent reduction. Dense aerial survey data with well-populated attributes compresses best; sparse clouds, or files whose header scale factors force high coordinate precision, compress less.
Can I keep working with the LAZ file directly?
In most modern software, yes — QGIS, ArcGIS Pro, CloudCompare, PDAL and lidR all read LAZ natively, so you can usually compress and delete the LAS. The tradeoff is a small CPU cost on every read, since points are decompressed on the fly.
Is LAZ an open format, or am I locking my data up?
It is fully open. The LAZ specification and the reference LASzip implementation are public and open source, and multiple independent implementations exist including laz-perf and PDAL. Compressing to LAZ does not create a vendor dependency.
Should I use LAZ or COPC?
Use LAZ for archiving and file transfer, and COPC when you need to stream or render subsets from cloud storage without downloading the whole file. COPC is a reorganised LAZ — same compression, spatially indexed — so it is a distribution format rather than a replacement for LAZ.

Need to go back? Convert LAZ to LAS.