{{ summaryTitle }}
{{ summaryValue }}

{{ summaryLine }}

Profile{{ profile.label }} PrivacyLocal only Warnings{{ computation.values.warning_count }}
One .xlsx file · 25 MB compressed input · 120 MB expanded-package limit.
{{ sourceFile ? sourceFile.name : 'Drop one XLSX here' }}
{{ sourceFile ? fileMeta : 'or browse from this device' }}
Image optimization can be lossy. PNG transparency is preserved; review important pictures and charts in Excel.

{{ workflowMessage }}

The neutral default keeps the package preview unchanged.
{{ remove_thumbnail ? 'Remove preview when present' : 'Keep preview thumbnail' }}
Workbook result
{{ artifactLabel }}
{{ artifactUse }}
Original
{{ formatBytes(computation.values.source_bytes) }}
Verified rebuild
{{ formatBytes(computation.values.output_bytes) }}
Images optimized
{{ computation.values.changed_media_count }}
Parts checked
{{ computation.values.checked_part_count }}
SHA-256 {{ outputSha256.slice(0, 12) }}…

The chart renderer is unavailable. The same byte counts remain in Workbook result and Verification ledger.

CategoryItemOutcomeEvidenceCopy
{{ row.category }}{{ row.item }}{{ row.outcome }}{{ row.detail }}
Online File Compressor Compress one local file into a compatible archive or stream and review size change with split delivery plus SHA-256 integrity before downloading.
PDF Compressor Compress a PDF locally in your browser, compare structural and production estimates, and catch encryption or image-quality risks before download.
XLSX to CSV Converter Convert one Excel worksheet to CSV in your browser, choose formula and hidden-data handling, and review warnings before download.
File to PDF Converter Turn images and text sources into local PDF output while preflighting Office files for renderer needs, layout risks and fidelity limits.

An XLSX workbook is a ZIP-based package of worksheets, formulas, styles, relationships, charts, images, and other parts. A large workbook may therefore owe most of its size to a few high-resolution pictures, or it may contain data and features that image compression cannot meaningfully reduce.

Picture size is governed by two separate quantities: pixel dimensions and encoded bytes. Reducing the longest edge lowers the number of pixels that must be stored. Re-encoding a JPEG can reduce bytes even when its dimensions stay the same, although stronger compression may soften text, thin lines, or chart labels. PNG is better suited to transparency and sharp graphic edges, so retaining its format avoids replacing transparent areas with an unwanted background.

Size source Likely effect of compression What needs review
Large JPEG or PNG pictures Often the largest opportunity for savings. Small labels, screenshots, diagrams, and print quality.
Workbook preview thumbnail Usually a modest saving when removed. The file preview shown by document browsers or file managers.
Cells, formulas, styles, and shared strings Repackaging may change ZIP overhead, but these parts are not image-compression targets. Calculated values, number formats, merged cells, and sheet order.
Pivot caches, embedded objects, external links, or data-model parts Preserving them protects workbook behavior but may limit savings. Refresh behavior, linked data, controls, and embedded content.

A smaller package is not automatically a better workbook. Compression is useful only when the rebuilt file opens correctly and important pictures remain readable. Workbooks with digital signatures need a different workflow because rewriting any signed package part can invalidate the signature. Macro-enabled files also require macro-aware handling rather than conversion through an XLSX path that cannot carry macros.

The safest review compares both structure and appearance. Package checks can confirm that sheets, formulas, styles, relationships, and unselected parts stayed intact. Excel still provides the final visual check for pictures, charts, previews, and advanced features that a structural comparison cannot judge.

How to Use This Tool:

Choose an image profile that fits the workbook's destination, then treat the verification results and an Excel review as part of the compression job.

  1. Select one XLSX workbook that does not contain macros. The compressed file must be no larger than 25 MB, and its expanded package must stay within 120 MB.
  2. Choose an Image profile. Balanced is the general starting point; Compact favors smaller screen-sharing files, while Print retains more pixels and JPEG detail.
  3. Leave Workbook preview thumbnail unchanged unless removing the package preview is acceptable. This option does not remove worksheet pictures.
  4. Start compression and review any preserved-feature warnings. Unsupported picture formats and advanced workbook parts remain unchanged instead of being guessed at or discarded.
  5. Compare the source and output sizes, download the rebuilt workbook, and open it in Excel. Check every important sheet, formula, chart, picture, link, pivot table, and preview before replacing the source file.

Interpreting Results:

Saved bytes and Savings percent describe the rebuilt package, not a quality score. A result marked No gain means the rebuilt file was not smaller, often because eligible pictures were already compact or the new ZIP package offset small media savings.

The media decisions distinguish optimized pictures from unchanged, unsupported, or larger candidates. A re-encoded picture is accepted only when it saves at least 1,024 bytes; otherwise the original bytes are retained. This prevents a nominal “optimization” from increasing the workbook merely because a picture was processed.

Passing package checks raises confidence that the workbook structure survived, but it does not prove visual equivalence. Open the downloaded XLSX in Excel and inspect the content at the zoom level and print size that matter. Keep the source until that review is complete.

Technical Details:

SpreadsheetML stores the workbook as related package parts. Worksheets refer to drawings, charts, shared strings, styles, and other content through relationship records. Safe media optimization therefore changes only selected image parts and, when requested, the preview-thumbnail relationship and content-type entry.

Transformation Core:

The transformation follows a bounded inspect, optimize, rebuild, and verify sequence. Unselected content remains byte-for-byte unchanged.

Stage Rule Evidence retained
Inspect Reload the ZIP with CRC checks, reject unsafe paths, identify the main workbook and its relationships, and confirm an XLSX content type without macros. Package-part count, expanded bytes, sheet order, relationship inventory, and warnings.
Optimize media Process referenced JPEG and PNG images. Resize only when an image exceeds the selected longest edge; JPEG files of at least 100 KB may also be re-encoded at the selected quality. Original bytes, output bytes, and a decision for every supported or unsupported image target.
Apply thumbnail policy Remove only a non-shared package preview target and its relationship when removal is selected. Removed target and byte count, or a warning when no removable preview exists.
Rebuild Write the package with DEFLATE compression while storing rewritten image bytes in their original JPEG or PNG format. Final package bytes.
Verify Reload with CRC checks, compare the complete part inventory, confirm unselected parts are identical, and recheck sheets, formulas, styles, and relationships. Verification ledger and any preserved-feature warnings.

Formula Core:

Byte savings cannot be negative. When the rebuilt package is larger, saved bytes and the displayed percentage both resolve to zero.

Bsaved = max ( 0 , Bsource - Boutput )
S = Bsaved Bsource × 100

The percentage is rounded to two decimal places. Source and output sizes are measured in bytes after the rebuilt package has passed verification.

Image Profiles:

Profile Longest edge JPEG quality Typical tradeoff
Compact 1,280 px 72% Largest likely savings, with the highest risk to small picture detail.
Balanced 1,920 px 82% General sharing and ordinary screen review.
Print 2,560 px 90% More retained detail and usually smaller savings.

Rule Core:

Boundary Limit Reason
Compressed input 25 MB Bounds browser memory and processing time.
Expanded package 120 MB Limits decompression expansion.
Package entries 500 Bounds the part inventory and verification work.
Referenced images 40 Bounds image decoding and ledger size.
Pixels per image 24 million Rejects an individual image that is too costly to decode safely.
Total decoded pixels 80 million Bounds cumulative image memory.

Privacy Notes:

Workbook bytes are read, transformed, and rebuilt in the browser; they are not uploaded for compression. The downloaded result exists only when you save it. A local-processing claim does not remove the need to follow your organization's rules for confidential spreadsheets or to clear downloads from shared devices.

References: