The short answer
- 7Z is a binary archive format that bundles files with selectable compression methods and optional AES-256 encryption, with encrypted archives requiring the correct password.
- Use 7-Zip or another application or library compatible with 7Z. Official 7-Zip command-line builds are available for Windows, Linux, and macOS. Inspect the file list before extracting, enter the correct password if encrypted, and choose a controlled destination. Compatibility should be determined from the format and signature rather than the .7z suffix alone.
- A 7Z container has no defined executable active content, but it can contain arbitrary files, including programs. Scan extracted items and handle each according to its actual type. Crafted archives have caused excessive-memory denial of service and out-of-bounds memory corruption in parsers, so use updated software, sandboxing, and extraction resource limits. This supports a medium—not absolute—risk assessment.
7Z File: How to Open, Check, and Convert a 7-Zip Archive
A 7Z file is a container associated with 7-Zip. Its open codec architecture can use LZMA, LZMA2, PPMd, BZip2, Copy, BCJ, or BCJ2 and can store Unicode names, sizes, timestamps, Windows attributes, CRC values, and coder pipelines. A genuine archive starts at offset 0 with 37 7A BC AF 27 1C; PRONOM identifies the format as fmt/484.
Converting 7Z to ZIP or another archive normally means extracting and recompressing. File payloads can remain byte-identical when handled losslessly, but the destination may not preserve 7Z coder pipelines, solid layout, AES encryption, compressed headers, or every timestamp and attribute. For long-term access, Library of Congress guidance favors 7Z without passwords, encryption, or other protection.
How to open it
Use 7-Zip or another application or library compatible with 7Z. Official 7-Zip command-line builds are available for Windows, Linux, and macOS. Inspect the file list before extracting, enter the correct password if encrypted, and choose a controlled destination. Compatibility should be determined from the format and signature rather than the .7z suffix alone.
Use 7-Zip or another application or library compatible with 7Z. Official 7-Zip command-line builds are available for Windows, Linux, and macOS. Inspect the file list before extracting, enter the correct password if encrypted, and choose a controlled destination. Compatibility should be determined from the format and signature rather than the .7z suffix alone.
Converting 7Z to ZIP or another archive normally means extracting and recompressing. File payloads can remain byte-identical when handled losslessly, but the destination may not preserve 7Z coder pipelines, solid layout, AES encryption, compressed headers, or every timestamp and attribute. For long-term access, Library of Congress guidance favors 7Z without passwords, encryption, or other protection.
File safety
A 7Z container has no defined executable active content, but it can contain arbitrary files, including programs. Scan extracted items and handle each according to its actual type. Crafted archives have caused excessive-memory denial of service and out-of-bounds memory corruption in parsers, so use updated software, sandboxing, and extraction resource limits. This supports a medium—not absolute—risk assessment.
An unknown sender, a name ending in two extensions, or contents that do not match the extension — check before you open it.
Converting it
Converting 7Z to ZIP or another archive normally means extracting and recompressing. File payloads can remain byte-identical when handled losslessly, but the destination may not preserve 7Z coder pipelines, solid layout, AES encryption, compressed headers, or every timestamp and attribute. For long-term access, Library of Congress guidance favors 7Z without passwords, encryption, or other protection.
Convert a copy, never the original, then compare quality, metadata, and layout against what you started with.
Common questions
What is a 7Z file format and what is it used for?
A 7Z file is a binary archive container associated with 7-Zip. It bundles files and supports multiple compression methods, solid compression, Unicode names, compressed headers, and optional AES-256 encryption.
How do I open and extract a 7Z archive?
Open it with 7-Zip or a compatible archive application or library, review its entries, and extract them to a controlled folder. An encrypted archive also requires the correct password.
How do I open a 7Z file on Windows?
Use 7-Zip or another compatible Windows archive application. Inspect the listed contents before extraction, then select a destination; supply the correct password if the archive is encrypted.
How do I extract a 7Z archive on macOS?
Use the official 7-Zip command-line build for macOS or another 7Z-compatible archive application. Extract to a chosen folder and treat each resulting file according to its own type.
How do I open a 7Z file on a phone?
Use a mobile archive application that explicitly supports 7Z. Compatibility cannot be inferred from the filename alone, and encrypted content cannot be decrypted without the correct password.
Why will my 7Z archive not open or extract?
Check that its first six bytes are 37 7A BC AF 27 1C, use an updated compatible parser, and verify the password if encrypted. A matching suffix alone does not prove the file is a valid 7Z archive; parser failures may also reflect damaged or crafted input.
Should I use 7Z or ZIP for an archive?
Use 7Z when you need its selectable coder pipelines, solid compression, compressed headers, or AES-256 support. Use another format only after checking whether it preserves the features and metadata you need; conversion may discard 7Z-specific structures.
How do I convert a 7Z archive to ZIP, and what information can be lost?
Extract the 7Z contents and recompress them as ZIP. Payload bytes can remain unchanged with lossless handling, but coder pipelines, solid layout, AES encryption, compressed headers, and some timestamps or attributes may not survive.
Can a 7Z file contain malware or unsafe programs?
Yes. The container does not define executable active content, but it can hold programs or other unsafe files. Scan extracted items, use updated software, and consider sandboxing and resource limits for untrusted archives.
What compression methods, encryption, and file sizes does the 7Z format support?
Its open codec architecture supports LZMA, LZMA2, PPMd, BZip2, Copy, BCJ, and BCJ2. It also supports AES-256 encryption, solid compression, compressed headers, Unicode names, and very large files.
Related formats
Sources
7z Format description (7zFormat.txt) · Official 7-Zip specification repository
7z Format · Official 7-Zip developer website
7z File Format · Library of Congress digital-format registry
PRONOM fmt/484: 7Zip format · The National Archives PRONOM registry
CVE-2021-35516 · NIST National Vulnerability Database
CVE-2026-20215 · NIST National Vulnerability Database
Recommended Formats Statement – Datasets · Library of Congress preservation guidance