How far apart should shelves be, and how deep?

Book shelves should be 12 in (30 cm) apart from the top of one shelf to the top of the next, and 10 in (25 cm) deep. Most guides give 8 to 12 in without saying whether that is a clear gap or a pitch. This page fixes the datum, then works the spacing out from a printer's trim sizes and a library survey of 350,000 books. Span, the other half of a shelf, is in shelf span, thickness and sag.

Spacing is shelf top to shelf top, and the board is why figures disagree#

There are two ways to state shelf spacing, and published figures use both without saying which.

• Pitch, or centres: from the top surface of one shelf to the top surface of the next. This is what you set out on a side panel and what a row of pin holes fixes.
• Clear height: from the top of one shelf to the underside of the shelf above. This is what the book has to fit into.

The difference is one board thickness. With a 3/4 in (19 mm) shelf, 12 in centres give 11.25 in (29 cm) clear, so a guide that says "10 to 11 in between shelves" and one that says "12 in apart" describe almost the same bookcase. Library steel shelves are 3/4 in thick too, by Spacesaver's cantilever stack specification, so the arithmetic carries straight across.

Figures here give the pitch first and the clear height second, measured as the site's measuring method asks, from a named face.

Book height plus 1.6 in: the allowance that produces 12 in#

A book has to come out as well as fit. On a full shelf you hook a finger over the head and tip it, which needs space above the tallest book.

When the University of Missouri special collections reorganised its oversize books, it allowed "1 cm for the shelf and 4 cm for easy retrieval", so books 27 to 29 cm (10.6 to 11.4 in) tall went on intervals of 32 to 34 cm (12.6 to 13.4 in), John Henry Adams reports in a 2023 paper in RBM. That 4 cm (1.6 in) is the allowance used here. With a 3/4 in board in place of a 1 cm one:

pitch = book height + 1.6 in + 0.75 in

Book heights come from trim sizes. IngramSpark, a large print-on-demand printer, offers paperbacks from 4 x 6 in up to 8.5 x 11 in and hardcovers from 5 x 8 in up to 8.5 x 11 in. A hardcover is taller than its trim: the boards overhang the pages by 1/8 in (3 mm) on all sides, says Bookmobile, a book printer, so a 6 x 9 in hardcover stands 9.25 in (23.5 cm) tall.

So 12 in is the pitch that takes every trade paperback and every hardcover up to 6 x 9 in with the full retrieval allowance. How much of a real collection that covers has been measured.

In 1935 Norman Kilpatrick and Henry Van Hoesen measured 350,000 books at Brown University and found that 75 per cent were 25 cm (9.8 in) tall or less. They set the oversize cutoff at 26 cm (10.2 in) and recommended shelving 86 to 88 in (2.18 to 2.24 m) tall where seven shelves of 26 cm books were wanted: 12.3 to 12.6 in (31 to 32 cm) a shelf, about where the table lands. NISO now recommends library uprights of 84 or 90 in (2.13 or 2.28 m), Adams notes, and seven shelves on 84 in is 12 in each.

An 8.5 x 11 in hardcover fills 12 in centres exactly#

The test is always the same: clear height must beat the tallest book on the shelf by at least 1 in (25 mm), and 1.6 in (4 cm) is better. Whole-case heights, widths and the vinyl case are in bookcase dimensions, and a study wall is planned in bookshelf and shelving dimensions.

Depth is the book's width, so 10 in holds every standard trim#

A book stands with its spine to the front, so the depth it needs is its width, not its height, plus the 1/8 in (3 mm) a hardcover's boards overhang at the fore-edge.

Depths are rounded up so the spine sits back from the edge. 6.14 x 9.21 in is the largest size IngramSpark prints on crème paper, the paper of most novels, so 8 in (20 cm) is enough for fiction.

Spacesaver's specification offers single-faced library shelving at nominal depths of 8, 9, 10 and 12 in (203, 228, 254 and 304 mm). A 9 in shelf takes an 8.5 x 11 in hardcover almost flush; 10 in sets its spine back. A 12 in shelf is 2 in deeper than any standard book needs, and that spare depth is what invites a second row behind the first. The storage and shelving hub sets out why a back row is worth about half a front one.

Depth barely changes sag: the shelf span calculator gives a 10 in shelf much the same span as a 12 in one.

Pin holes decide which pitch you can actually set#

Adjustable shelves sit on pins in a column of holes, and the holes come in fixed steps. Library steel uprights are slotted every 1 in (25 mm) by the Spacesaver specification, so 12, 13 or 14 in can be set exactly. European cabinet carcasses are commonly drilled on the 32 mm system, so every pitch is a whole multiple of 32 mm (1.26 in). A 12 in pitch is 305 mm, which is not on the list.

The useful coincidence is the 320 mm row. Its tallest book, 262 mm (10.3 in), is almost exactly the 26 cm oversize cutoff Kilpatrick and Van Hoesen drew from their 350,000 books. On a 32 mm carcass, 320 mm is the library's "regular" shelf and 352 mm the oversize one. The step below, 288 mm, holds a 6 x 9 in hardcover (235 mm) with 35 mm over it: tight, but workable. Rounding 12 in to 300 mm instead is the near-miss described in imperial and metric: the dimension systems that collide.

Pantry cans are 3 in across, so 12 in is four rows on paper#

Cans also have published dimensions. US can sizes are written as diameter by height in inches and sixteenths: a 300 x 407 can holds about 15 oz and is 3 in (76 mm) across and 4 7/16 in (113 mm) tall. The sizes below come from a table of industry can sizes. The pitches apply the same 1.6 in (4 cm) allowance as the books and a 3/4 in board; that choice is the site's own, since cans are lifted up and out in the same way.

Two rows of that table hide a trap. Four 300 x 407 cans take 12 in with no allowance at all, so they fit only on a shelf that really is 12 in deep. A shelf cut from a nominal 1x12 board is 11.25 in (286 mm), which holds three. A No. 10 can, the catering size, needs 12.38 in (314 mm) for two rows, so a 12 in shelf holds one row with nearly 6 in (15 cm) of nothing behind it. Measure the real depth first, then divide it by the diameter of the can you buy most.

Shoes are worked the same way in shoe storage dimensions, linen over a machine in laundry shelving and cabinet heights, and bins and power tools are in garage shelving and overhead storage.

Above 48 in, a shelf stops counting as accessible#

The 2010 ADA Standards put the high forward reach at 48 in (1,220 mm) maximum and the low reach at 15 in (380 mm) minimum (308.2.1). Reaching over an obstruction deeper than 20 in (510 mm), the high limit drops to 44 in (1,120 mm) (308.2.2); a side reach over something up to 34 in high and 24 in deep is held to 46 in (1,170 mm) (308.3.2). Storage must meet "at least one of the reach ranges specified in 308" (811.3), and where it is provided in accessible spaces, "at least one of each type" must comply (225.2).

The arithmetic is unforgiving. An 84 in (213 cm) bookcase on a 4 in (10 cm) plinth at 12 in centres has shelf surfaces at 4, 16, 28, 40, 52, 64 and 76 in. Three of the seven, at 16, 28 and 40 in, fall inside 15 to 48 in. The pitch that suits the books leaves more than half the case outside the accessible range.

Library stacks escape this: "self-service shelving shall not be required to comply with 308" (225.2.2). A home does not. Put what is used daily between 15 and 48 in and treat everything above as archive. The reach rules across the US, UK and Australia are on the accessible design hub, and the shelf height over a worktop is in upper cabinet and backsplash heights.

Where these figures stop applying#

Books shelved flat. Everything above assumes books stand upright. Adams found that only about 26 per cent of one folio collection needed flat storage for preservation, and puts the space gain of upright over flat shelving at "up to 600 percent". Kilpatrick and Van Hoesen gave books over 45 cm (17.7 in) a class of their own.

Old books and records. Trim sizes describe what one printer offers today; for an inherited library the Brown survey's 26 cm (10.2 in) line is the better place to split a collection. A 12 in (30 cm) LP outgrows every figure here.

Hanging and drawers. A shelf over a rod is placed from the rod, as hanging rod heights, lengths and capacity explains, and small folded items often store better in a drawer than on a pitch; box heights and runner allowances are in drawer sizes, depths and internal capacity.

Terms used here are defined in the glossary, and the reference works behind them are listed under standards and codes.