Clamshell Box Calculator
Box board dimensions from book measurements.
About this calculator
A clamshell (drop-spine) box protects a book inside two interlocking board trays — a base tray holding the book and a slightly larger lid tray that drops down over it — joined by a spine wall. This calculator works outward from your book's height, width, and closed thickness: it first adds a small clearance (2mm) to get the base tray's interior dimensions, then builds the base's floor and four wall pieces around that, sized to account for the board thickness you specify. The lid tray is calculated to fit around the finished base tray's exterior with 1mm of clearance, and its depth is set to roughly two-thirds of the base tray's depth, following a standard clamshell design proportion.
Altogether the calculator works out to 10 total board pieces (2 floors plus 8 walls across both trays) and estimates total davey board area for material planning, along with covering cloth (bookcloth or paper) area for both trays, assuming a fixed 20mm turn-in allowance for wrapping the cloth around each tray's edges. The reported closed box dimensions tell you the overall footprint of the finished, assembled box. Because the depth proportions and clearances here follow one common convention rather than a single universal standard, if you're matching an existing box design or unusually thick book boards, treat these as a solid starting point and verify tray depth against your actual book thickness before cutting expensive archival board.
Inputs
Results
Box height (mm)
231
Box width (mm)
166
How to Use This Calculator
- Measure the book's height, width (cover to fore-edge), and total closed thickness in millimeters.
- Enter your davey board thickness — 2 mm is standard for most clamshell boxes.
- Read the overall closed box dimensions (height, width, and depth) to verify it fits your storage requirements.
- Use the total board pieces and board area outputs to cut your davey board efficiently.
- Use the cover cloth area in cm² to estimate how much bookcloth to cut for covering both trays.
How the result changes with Book height (mm)
| Book height (mm) | Box height (mm) | Box width (mm) |
|---|---|---|
| 110 | 121 | 166 |
| 165 | 176 | 166 |
| 330 | 341 | 166 |
| 550 | 561 | 166 |
What each input means
- Book height (mm)
- Height of the book to be enclosed.
- Book width (mm)
- Width of the book (cover to fore-edge).
- Book thickness (mm)
- Total thickness of the closed book including covers.
- Board thickness (mm)
- Thickness of the davey board for the box. 2 mm is standard.
What each result means
- Box height (mm)
- Overall height of the closed box.
- Box width (mm)
- Overall width of the closed box.
- Box depth (mm)
- Overall depth (thickness) of the closed box.
- Board pieces to cut
- Total number of board pieces (floors + walls).
- Total board area (cm²)
- Total board area for material estimation.
- Cover cloth area (cm²)
- Approximate bookcloth needed for both trays with turn-in.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersBook height (mm) = 220, Book width (mm) = 155, Book thickness (mm) = 25, Board thickness (mm) = 2 = 4 input(s) provided
- Calculate Box heightBox height = lidInteriorH + 2 * boardThicknessMm231 = 231
- Calculate Box widthBox width = lidInteriorW + 2 * boardThicknessMm166 = 166
- Calculate Box depthBox depth = baseInteriorD + lidInteriorD + boardThicknessMm47 = 47
- Calculate Board pieces to cutBoard pieces to cut10 = 10
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why is the lid tray's depth only about two-thirds of the base tray's depth?
The calculator sets lid interior depth to roughly 0.67 times the base interior depth (with a 5mm minimum), following the standard clamshell proportion where the lid only needs to cover down over the base tray's walls, not enclose the full book thickness a second time. The base tray does the deep holding of the book; the lid just needs enough depth to seat securely over the base's exterior.
What's the difference between the "clearance" and "lid clearance" values used in the calculation?
The 2mm clearance is added to the book's own dimensions to size the base tray's interior, so the book isn't a snug, hard-to-remove fit. The separate 1mm lid clearance is added when sizing the lid's interior around the base tray's finished exterior, so the lid tray slides over the assembled base without binding — they solve two different fitting problems at two different assembly stages.
Why does the calculator report exactly 10 board pieces regardless of my book's dimensions?
Every clamshell box in this model uses the same piece-count structure: one floor plus four walls for the base tray, and one floor plus four walls for the lid tray, totaling 10 pieces. Your book's dimensions change each piece's individual size, not how many pieces the design requires — the clamshell drop-spine structure itself is fixed.
How is the covering cloth area estimated, and does it include enough for wrapping edges?
Yes — the cloth dimensions add a fixed 20mm turn-in allowance on top of each tray's own exterior dimensions, since covering cloth needs to wrap around the board edges and fold onto the inside surfaces to be glued down cleanly. The reported area covers both trays combined, so budget your bookcloth purchase against that combined figure rather than doubling a single-tray estimate yourself.
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