Calibrate printer size on Mac for accurate photo prints.

Direct answer. In Inspector → Page, pick a printer. For a printer with no saved record, choose Calibrate… and click Print Test Page to print one ruler rectangle at forced 100%. If a record already exists and you need a new sample, open Edit Calibration… and click Reprint Test Page. Measure the full width (X) and height (Y) with a ruler, type Measured Width (X) and Measured Height (Y), then click Save Calibration. The per-axis correction saves per printer name, toggles with Use Physical Calibration, and applies to printed Frames and Content — not Page size, color, or DPI.

When calibration helps — and when it does not

Calibration helps when one printer consistently prints every Frame slightly larger or smaller on one axis, after paper match and Scale to Fit are clean. It does not fix irregular feed, clipping, borderless expansion, low effective DPI, or color drift. Run the 100% checklist first; if output still drifts by a steady fraction on one axis of one printer, calibration is the next step.

The 6-step calibration

1. Select the printer in the workspace. In Inspector → Page, choose the printer you want to calibrate. The Calibrate… button stays disabled until a printer is selected.
2. Confirm paper and driver prerequisites. Set the Page paper size to the loaded paper, set Scale to 100% in the macOS print panel, and turn off any driver auto-scale or borderless expansion option where supported so the test print is not silently rescaled.
3. Print the test Page. For a printer with no saved record, open Calibrate… and click Print Test Page to draw the first ruler test Page. If a record already exists and you need a new sample, open Edit Calibration…; the dialog opens at the measurement step, where Reprint Test Page produces a fresh test Page. The test Page draws at forced 100% with X on the top edge and Y on the left edge of one rectangle. If the dialog says the printable area is too small, switch to a larger paper or a different printer.
4. Measure the printed rectangle. Measure the full width (X) and full height (Y) of the printed rectangle with a physical ruler — not the sheet, a tick interval, or a photo — and record both values in the unit PrintExactly displays.
5. Enter the measurements and save. In Step 2, type Measured Width (X) and Measured Height (Y). PrintExactly shows live percentages and only accepts positive measurements that keep both factors between 80% and 120%. Choose Save Calibration — the record preserves any existing enabled or disabled state; a brand-new record is enabled by default.
6. Pick the intended printer, then verify with a regular layout. With Use Physical Calibration on in Inspector → Page, print a regular layout at a Frame size you can measure with a ruler. The per-printer correction is baked into the rendered PDF, so the print dialog warns only when the printer you choose differs from the saved calibration used for the output. Return to the workspace and select the intended printer so the output uses the matching calibration, rather than printing with a mismatched printer.

Independent axes and the per-axis formula

Each axis is corrected independently. The dialog displays the scale as a percentage so you can sanity-check the math, but you always type the measurement, not the percentage.

• Horizontal Scale (X) = Reference X ÷ Measured X
• Vertical Scale (Y) = Reference Y ÷ Measured Y

Illustrative example, not a guarantee. Reference X = 100 mm and Measured X = 99 mm gives 100 ÷ 99 ≈ 1.0101, about 101.01%. Reference Y = 100 mm and Measured Y = 100 mm is exactly 100% — no change. PrintExactly applies these factors inside the 80–120% range and treats anything outside it as invalid. The reference lengths are not a universal 100 mm or 4 in constant — they depend on the printer-reported printable area — so use the values the dialog shows for the current printer and paper.

Manage, disable, reset, and recalibrate

• Use Physical Calibration — toggle in Inspector → Page turns the saved record on or off without deleting it.
• Edit Calibration… — reopens the sheet so you can re-measure and overwrite the saved values.
• Reset Calibration — removes the saved record for the active printer.
• Reprint Test Page — always draws an uncorrected reference; it does not prove the corrected output. Print a regular layout at a measurable Frame size instead.
• Recheck when you switch paper or driver settings, rename the printer, or move to a different printer. Records are local to the Mac and keyed by printer name.

Troubleshooting

• The printer is unavailable, or Calibrate… is disabled / says "Select a printer in the Page section before calibrating." Pick a printer in Inspector → Page first. When the selected printer is unreachable, printing the test Page is disabled but Edit Calibration… and Reset Calibration still work on the saved record.
• "The selected paper or printable area is too small for a calibration test Page." Switch to a larger paper or a different printer — the test Page needs room for its centered rectangle.
• "Enter positive measured lengths that keep both scale percentages between 80% and 120%." Re-measure the full printed rectangle — not the sheet or a tick interval — and type the value in the unit PrintExactly shows.
• The print dialog warns that the chosen printer differs from the saved calibration used for the output. The per-printer correction is baked into the rendered PDF. Return to the workspace and choose the intended printer so the output uses the matching calibration instead of a mismatched one.
• Correction still leaves drift. Paper feed, mechanical tolerance, ink spread, driver scaling, and borderless expansion sit outside what calibration absorbs. Re-run the 100% checklist before assuming the record needs another change.
• I renamed the printer or moved to a new printer. The record is keyed by printer name, so renaming or switching hides it. Switch back to read it, or recalibrate.

Frequently asked questions