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How wide is my spine?

By Mike HeatonUpdated October 20268 min readPerfect boundFor designers
The short answer

On a perfect bound book, it’s set by your inside page count and paper. 40 inside pages on 130gsm silk, for example, gives a 3mm spine.

Finish your inside pages first, because the spine changes with the page count. Use the calculator below, and we’ll confirm the exact width at your free file check.

Work out your spine, cover and page sizes in one go

Pick your book size, tell us how many inside pages you have and which paper they’re printing on. We’ll give you the spine width and the exact dimensions to set up both PDFs.

The pages between the covers. Don't count the 4-page cover.

3mmspine width

A5 book · 40 inside pages · 130gsm Silk or Gloss

PDF 1 · Cover spread
210 × 299mm216 × 305mm with 3mm bleed
PDF 2 · Inside pages
210 × 148mm216 × 154mm with 3mm bleed
3mm spineBACKFRONT148mm148mm210mmDASHED LINE = 3MM BLEED299mm wide · 216 × 305mm with bleed

Your inside pages PDF should contain exactly 40 pages in reading order — no covers.

Three things decide your spine width

A perfect bound spine is simply the stack of paper inside the cover, so it grows with every page you add and every step up in paper weight. Here’s all you need to read the chart.

1Count your inside pages

That’s every page between the covers. A “4 + 40pp” book has a 4-page cover and 40 inside pages, and the 40 is the number you want.

2Know your inside paper

130gsm silk, 120gsm uncoated, 170gsm gloss… the weight and finish set how thick each sheet is. Silk and gloss of the same weight share a spine size.

3Read off the spine

Find your page count in the chart, run across to your paper, and that’s your spine in millimetres. Between two rows? Use the nearest, or the calculator above.

Spine widths by page count and paper

All figures are in millimetres, rounded to the nearest whole millimetre, for perfect bound (PUR) books. Only your inside pages count. Silk and gloss of the same weight share a column.

On a slim book, go up a paper weight

28 inside pages on 130gsm or 150gsm silk make a spine of just 2mm, which is very slim. We'd suggest 170gsm: it gives the book more body and takes the spine to 3mm.

Longer books, odd page counts, or an exact figure

Beyond 400 pages, or for a page count that isn’t in the chart, the spine follows a simple line: a fixed thickness per page plus a small constant. Round to the nearest whole millimetre.

pages × k + cyour spine width in millimetres, using k and c for your paper
5mm64 inside pages on 120gsm Uncoated: 64 × 0.0705 + 0.54 = 5.05, rounded to 5mm
Spine formula values by inside paper
Inside paperk (mm per page)c (constant)≈ per leaf
130gsm Silk / Gloss0.04901.030.098mm
120gsm Uncoated0.07050.540.141mm
150gsm Silk / Gloss0.06270.680.125mm
140 / 150gsm Uncoated0.08010.870.160mm
170gsm Silk / Gloss0.07330.520.147mm
170gsm Uncoated0.09670.750.193mm
k is how much each inside page adds, and c is a small constant. The last column is the thickness of each leaf (two pages).

Turning your spine size into a cover spread and inside pages

A perfect bound book needs two PDFs. The cover is one landscape spread with the spine running down the middle. The inside pages are single pages, one after another, in reading order. Here’s the maths, with H for height, W for width and S for spine, all in millimetres.

ARTWORK SIZE WITH BLEED · (H + 6) × (W + S + W + 6)BACK COVERtrimmed width WFRONT COVERtrimmed width WSPINE · S3mm3mmWSWHTrimmed cover spread = H × (W + S + W) · Spine never gets bleed — only the four outside edges do
Back cover + spine + front cover, left to right, on one page. Add 3mm bleed to every outside edge (never around the spine).
PDF 1The cover spread

H × (W + S + W)mm, or (H + 6) × (W + S + W + 6)mm with the 3mm bleed on each outside edge. Back cover on the left, spine in the centre, front cover on the right.

Supply a 1-page PDF, or 2 pages if your inside front and back covers are printed too.

PDF 2The inside pages

H × Wmm as single pages, not spreads, or (H + 6) × (W + 6)mm with bleed.

The PDF should contain every inside page in reading order and nothing else: 40 inside pages means a 40-page PDF. Leave the covers out.

Our cover file guide walks you through building the spread step by step, with ready-made templates. Designed your inside pages as spreads? Our free Spread Splitter turns them into single pages in about a minute.

Two real books, start to finish

A5 · 40 inside pages · 130gsm Silk3mm spine

From the 40pp row, 130gsm Silk / Gloss column.
Cover spread: 148 + 3 + 148 = 299mm wide, so 210 × 299mm
Cover spread with 3mm bleed: 216 × 305mm
Inside pages: 210 × 148mm (216 × 154mm with bleed)
Inside pages PDF: 40 pages

279 × 216mm · 140 inside pages · 170gsm Uncoated14mm spine

From the 140pp row, 170gsm Uncoated column.
Cover spread: 216 + 14 + 216 = 446mm wide, so 279 × 446mm
Cover spread with 3mm bleed: 285 × 452mm
Inside pages: 279 × 216mm (285 × 222mm with bleed)
Inside pages PDF: 140 pages

Standard trimmed sizes

Standard trimmed page sizes, height × width, with and without 3mm bleed
SizeTrimmed page (H × W)Inside page artwork with 3mm bleed
A6148 × 105mm154 × 111mm
A5210 × 148mm216 × 154mm
A4297 × 210mm303 × 216mm
Square210 × 210mm216 × 216mm
Square250 × 250mm256 × 256mm
Square294 × 294mm300 × 300mm
US Letter279 × 216mm285 × 222mm
Height first, as we quote them. Custom sizes work exactly the same way: take your trimmed height and width and add 6mm to each for the bleed size.

Make the spine work hard on the shelf

The spine is the first thing most people see once your book is shelved. A few habits keep it looking sharp, whatever the binder does on the day.

Keep spine text small and centred

Binding has a natural tolerance of a millimetre or so. Text that sits comfortably inside the spine, with clear space either side, stays on the spine even if the book folds a fraction off centre.

Under 5mm? Leave the text off

On a spine narrower than 5mm there simply isn’t room for lettering to sit safely, and it risks sliding round onto the front or back cover. Let colour or a pattern do the talking instead.

Mind the glue on your first and last pages

The cover is glued to your first and last inside pages, so keep anything important, such as text, logos and faces, 10–12mm clear of the spine on those two pages. On every other page, 6–8mm is plenty.

Images that cross the spine

A photo running from the back cover to the front looks brilliant. Just remember a few millimetres disappear into the curve of the spine, so don’t put a face or a headline right on the fold.

Before you set up the file

Stapled booklets have no spine

If your booklet is wire stitched (stapled), the whole thing is one PDF of single pages at the trimmed size plus 3mm bleed all round. No spread, no spine, nothing to calculate.

Hardbacks use different maths

A case bound cover wraps around thick boards and turns in over the edges, so the chart above doesn’t apply. Tell us your spec and we’ll send you the exact cover dimensions. Our hardback set-up guide explains the files, including printed endpapers.

A guide for artwork, confirmed at your file check

Paper varies slightly from batch to batch, so a millimetre either way is normal. We confirm the final spine at your free file check, and if it needs a nudge we’ll tell you before anything prints.

Cover weight doesn’t change it

The spine is set only by the number and weight of your inside pages. Swap a 300gsm cover for 350gsm and the spine stays exactly the same, so choose your cover for feel and finish, not spine maths.

Spine size questions

What is the minimum page count for a perfect bound book?

32 pages in total: a 4-page cover plus 28 inside pages. Below that the spine is too thin to glue reliably, which is why the chart starts at 28 inside pages. Fewer pages than that? A stapled booklet is the answer.

My page count isn’t in the chart. What do I do?

Take the nearest row. If you have 62 pages, the 60pp and 64pp rows tell you everything you need. For an exact figure, pop your numbers into the calculator or use the formula: pages × k + c, rounded to the nearest millimetre.

Do silk and gloss papers have different spine sizes?

Not in practice. Silk and gloss of the same weight are the same base sheet with a different surface, so they share a column in the chart. Uncoated papers are bulkier, which is why 120gsm uncoated makes a thicker spine than 130gsm silk.

Does the cover paper change the spine width?

No. The spine is set purely by the number of inside pages and the paper they’re printed on. The cover simply wraps around that block, whatever its weight.

Do I add bleed to the spine?

No. The 3mm bleed goes on the outside edges of the cover spread only: top, bottom, left and right. The spine sits inside the spread, so it never gets bleed of its own.

Will you check my spine before printing?

Always. Every job gets a free file check, and the spine width is one of the first things we look at. If your page count or paper changes after you’ve set up the cover, just tell us and we’ll give you the new figure.

Still not sure? Send us the file.

We check every file for free: spine, bleed, page order, the lot. If anything needs changing, we’ll tell you exactly what before anything goes near a press.

Get a quote
Mike Heaton
Written by Mike HeatonMike answers most of the calls at Ex Why Zed, so the questions here are the ones he hears every week. We’ve been helping people get their work into print since 2006.
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Related answers

Set up your fileHow do I set up a perfect bound cover?As one spread: back cover, spine and front cover, left to right, plus a second page for the inside covers if they're printed. Add 3mm bleed…Read the guideSet up your fileDo you have cover templates?Yes, for A4, A5 portrait, A5 landscape and 210 × 210mm books, with the most common spine widths. Download them from our cover file guide.Read the answerPlan your projectWhat's the minimum page count for a perfect bound book?32 pages in total: a 4-page cover plus 28 inside pages. Any fewer, and a stapled booklet is the way to go.Read the answerSet up your fileHow far from the spine should I keep text?Keep text 6–8mm from the spine side of each page, and 10–12mm on the first and last inside pages, where the cover is glued on.Read the answerSize, paper & coversWhat paper weight should I choose?Most inside pages sit between 115gsm and 170gsm: 130gsm silk or 115–120gsm uncoated is standard. Covers are usually 300gsm. 170gsm is the…Read the answerSet up your fileHow do I set up files for a hardback?Send a cover wrap (your cover plus extra to fold round the boards), your inside pages as single pages, and two endpaper files if your…Read the guide
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