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EPUBIO · OPEN BOOK TOOLS

Five clear tools for your book.

Validate ISBNs, plan book length, calculate spine and cover dimensions, or see which editions need attention after a change. No upload, account or hidden assumptions.

  • No file leaves your device
  • Every calculation is visible
  • Free and without an account

TOOL · 01

Estimate spine width transparently

A production-ready cover needs a spine width. Here you see both the result and the assumption behind it.

Formula usedRound page count up to an even number ÷ 2 × paper thickness = estimated spine width

Estimated spine width

12.00 mm

First estimate for cover planning

sheets
120
Calculation
120 × 0.100 mm

Why paper thickness matters

Two book pages sit on one sheet. Its actual thickness depends on paper, bulk, grain direction and printing process, so the sheet thickness is entered explicitly.

Important before print approval

This result is an estimate, not production approval. The template and binding calculation supplied by your printer always take precedence. Binding, paper compression and provider rules may change the final measurement.

Next step

See how the book block, bleed and cover work together in epubio's print preparation guide.

Prepare print-ready files

TOOL · 02

Validate an ISBN and its check digit

Enter an ISBN-10 or ISBN-13 with or without hyphens. The complete validation runs in your browser.

Spaces, hyphens and an initial “ISBN” label are removed for the calculation.
Hyphen groups are not reconstructed because that requires current allocation ranges from the responsible ISBN agencies.

Ready for your ISBN

Once entered, you will see the format, normalized value and check-digit result.

TOOL · 03

Plan book length from word count

A realistic range for early planning, with visible assumptions instead of a falsely precise page count.

Estimated total extent

266–356 pages
Planning value
304 pages
Realistic range
266–356
Text-density assumption
233–317 / pages

Transparent calculation

  1. 01

    Base for trim size and structure135 × 215 mm · Predominantly continuous prose · 275 / pages

  2. 02

    Planning corridor± 15 % · 233–317 / pages

  3. 03

    Text pages80,000 ÷ 317–233

  4. 04

    Additional pages and even final count+ 12 · 266–356 pages

TOOL · 04

Calculate the full size of your print cover

Calculate the outside dimensions of a flat cover from trim size, spine width and bleed. Every value stays locally in your browser.
Dimensions in millimetres
Calculated full size
Total width288mm
Total height221mm
Width
(2 × 135) + 12 + (2 × 3) = 288 mm
Height
215 + (2 × 3) = 221 mm

TOOL · 05

What changes when your book changes?

Select one or more changes. The simulator translates them into clear tasks for EPUB, print, metadata and other editions.

What did you change?

RELEASETWIN

Typical impact

The strongest impact across your selection is shown for each edition.

2 rebuild · 3 review
EPUB fileThis edition contains the changed element or directly depends on it.
Rebuild
Print PDF · interiorThis selection normally does not require a new file.
Unchanged
Print coverThis edition contains the changed element or directly depends on it.
Rebuild
Store metadataThis edition may be indirectly affected or needs reconciliation.
Review
Sample & previewThis edition may be indirectly affected or needs reconciliation.
Review
Audiobook stateThis edition may be indirectly affected or needs reconciliation.
Review

ReleaseTwin maps dependencies

A new cover does not automatically change the book block. Edited text, however, can affect the EPUB, print PDF, preview and audiobook script. ReleaseTwin makes these relationships visible.

Simulation, not project validation

This preview does not know your specific book. It shows typical effects. In the epubio workspace, ReleaseTwin checks the actual project state and connects changes to existing editions.

The principle behind it

ReleaseTwin keeps changes, validation and editions connected and traceable.

Explore ReleaseTwin

DELIBERATELY CLEAR

No black box. No false precision.

Good book production starts with decisions you can understand. These tools show their logic and state clearly where a printer or a real project validation must take over.

01

Local

Inputs and results stay in your browser. No book data is uploaded.

02

Explainable

Formulas, assumptions and likely consequences sit next to the result.

03

Actionable

Every result leads to the relevant production step instead of a dead end.

FROM TOOL TO WORKFLOW

Your book needs more than isolated calculators.

epubio connects manuscript, EPUB, print, validation and publication in one guided production path.

Start a book project