Flexo repeat length: gear pitch, cylinder OD, and the references prepress shops actually get wrong
Flexo repeat length is the printed circumference of one image around the press cylinder — but which circumference depends on the reference. Here's gear pitch vs cylinder OD vs effective repeat, how each one interacts with plate distortion, and where shops lose plates by mixing them up.
Flexo repeat length is the printed length of one complete image around the plate cylinder — the distance the web travels for one full revolution of the cylinder at the plate surface. It sets the maximum image size in the press direction, it drives the plate distortion factor, and it’s the number every job ticket, plate order, and press setup sheet ultimately points back to.
The confusion isn’t what repeat length means. It’s which circumference a given number refers to. Most disputes between prepress, plate room, and the press floor come from three references being used interchangeably when they shouldn’t be.
The three references
A flexo plate cylinder has at least three circumferences depending on where you measure:
- Gear pitch circumference. Gear pitch (commonly 1/8” / 3.175 mm or 1/4” / 6.35 mm) multiplied by tooth count. This is a geometric property of the gear, not the print surface. On a 1/8” pitch press, a 120-tooth cylinder has a gear pitch repeat of 15.000” (381.0 mm).
- Bare cylinder OD circumference. The outer diameter of the metal cylinder, with no plate, no stickyback, no mounting tape. π × OD. Always smaller than the print surface circumference.
- Effective (print) repeat. Gear pitch circumference plus the buildup that sits above the gear pitch line — typically stickyback thickness plus plate thickness. This is the actual distance the printed image travels per revolution.
Most North American narrow-web flexo is set up so that gear pitch circumference = printed repeat when the correct plate gauge and standard mounting tape are used. That’s the whole point of the gear pitch convention: the gear is designed to mesh at the same circumference the print surface travels, given a specified plate-and-tape stack. Change the stack and the equality breaks.
Wide-web CI and some sleeve-based presses don’t follow the gear pitch convention at all. Repeat is published as an effective print repeat by the OEM, derived from the sleeve OD plus the plate-and-tape stack — and the prepress operator is expected to use that effective number directly.
How repeat length sets plate distortion
The distortion factor is:
Distortion % = (K / repeat length) × 100Repeat length goes in the denominator, so the same K constant produces different distortion at different repeats. A 67-mil plate (K ≈ 5.0 mm) gives:
| Repeat length | Distortion % |
|---|---|
| 250 mm | 2.00% |
| 381 mm (15”) | 1.31% |
| 500 mm | 1.00% |
| 762 mm (30”) | 0.66% |
| 1000 mm | 0.50% |
Use a different repeat reference than the one K was calibrated against and the distortion factor is wrong by the ratio of the two references. Most published K constants assume gear pitch repeat. If your shop measures off cylinder OD instead, a 0.5 mm reference shift on a 500 mm repeat is 0.1% of distortion — small per job, but it compounds with K-table error and shows up as a length miss at the press.
For the full distortion math, K constants per plate gauge, and the rest of the upstream errors, see flexo plate distortion: what it is and where shops get it wrong.
Variable repeat presses
Narrow-web label and flexible packaging presses increasingly use sleeve-based variable repeat. The plate cylinder is a hollow sleeve that slides onto a mandrel, so repeat is changed by swapping sleeves rather than swapping geared cylinders.
Variable repeat changes two things:
- There’s no gear pitch reference. Repeat is the effective print circumference of the sleeve plus the plate-and-tape stack — there is no tooth count to multiply.
- The same job can run on different repeats. A label printed at 16” on a Mark Andy can move to a 17” sleeve on a Nilpeter if a customer’s order quantity shifts the bottleneck. The artwork doesn’t change, but the distortion factor does.
Shops running sleeve presses have to track repeat per imaging instance, not per artwork. The MIS or job ticket has to record which sleeve the plate was distorted for, otherwise a re-run on a different sleeve gets the wrong plate.
The four places shops get repeat length wrong
1. Quoting off gear pitch when the press runs sleeves. A new customer’s job comes in spec’d at “15 inch repeat.” On a geared press that’s unambiguous — 120 teeth at 1/8” pitch. On a sleeve press, “15 inch” might mean 15.000” effective, or it might mean the customer’s old press had a 15.000” gear repeat that on their new sleeve press becomes 15.040”. The 0.040” difference is 0.27% — a visible registration error on a multi-station job.
2. Mixing units between metric and imperial. Most European flexo specs in millimeters. North America is mixed. A 381 mm repeat (15.000” exact) and a 381.5 mm repeat differ by 0.13% — enough to throw distortion when the prepress operator rounds wrong. The job ticket has to carry the repeat in its native unit, not a converted approximation.
3. Counting teeth instead of measuring the cylinder. Gear tooth count is reliable on geared cylinders that have not been re-ground or re-shimmed. A cylinder that’s been re-ground for runout has the same tooth count but a smaller print OD, which means the gear pitch convention no longer holds. Shops running older equipment should periodically verify the print repeat with a tape over the plate on press, not assume the gear tooth count is still accurate.
4. Stickyback or plate gauge substitutions that shift the stack. The gear pitch convention assumes a specified plate-and-tape stack height. Substituting a 0.020” stickyback for a 0.015” stickyback raises the print surface by 0.005”, which on a 15” repeat is about 0.10% additional stretch and a different effective repeat than the gear pitch. If the substitution isn’t recorded back into the job ticket and the distortion isn’t recomputed, the press operator catches a short repeat at first pull.
What repeat length is not
Repeat length is sometimes confused with:
- Image length. The image length is what’s actually printed; repeat length is the cylinder circumference. They’re equal only for full-bleed-around designs.
- Cutoff length. Cutoff is a sheetfed or web offset term. Flexo uses repeat.
- Web length per minute. That’s web speed, which is repeat × cylinder RPM.
- Plate length. A plate is usually slightly shorter than the repeat to leave a gap for mounting. The plate length is the imaged length after distortion compensation has been applied to the artwork.
The artwork-build length, the imaged plate length, and the printed repeat are three different numbers connected by the distortion factor. Treating them as the same number is the most common entry-level prepress mistake.
Where repeat length lives in the trade shop
Repeat length is a single field that touches every group in a prepress trade shop:
- Sales and CSR capture it at job intake, in the customer’s stated units, against the customer’s stated press.
- Prepress uses it to compute distortion and step-and-repeat layouts.
- Plate room orders and images plates sized to repeat minus the mount gap.
- The customer’s press team validates that the repeat the trade shop used matches the press the job will run on.
In shops still running on spreadsheets, this is a verbal handoff — one number copied four times. In a flexo-native MIS the repeat reference (gear pitch, cylinder OD, or effective sleeve repeat) is a typed field on the job ticket alongside the plate gauge and the K constant, so a substitution at the plate room triggers a re-distort instead of a silent length error at the press.
For more on this:
- Flexo plate distortion calculator — runs the distortion math in millimeters or inches, with K constants pre-loaded for the common plate gauges.
- Flexo plate distortion: what it is and where prepress shops get it wrong — the formula, the K table, and the four upstream errors that ruin print length.
- Prepress automation software for flexographic trade shops — where repeat and step-and-repeat sit in the workflow.
- Flexo prepress software for trade shops — the MIS that keeps repeat reference, plate gauge, and K constant on the job ticket.