CENTERMINT / TOOLS & GUIDES
Card centering calculator
Calculate left/right and top/bottom card centering from measured border widths. Free browser tool with a directional preview.
Enter four measured border widths in the same unit, such as pixels or millimeters. This tool calculates ratios; it does not detect borders in a photo.
Left / right
Top / bottom
Illustrative border preview
From border widths to a useful ratio
Left share = left ÷ (left + right) × 100. Top share = top ÷ (top + bottom) × 100. The other side is the remainder. For example, left 3 mm and right 2 mm produce 60.0 / 40.0. Reversing the inputs produces 40.0 / 60.0; the amount of imbalance is the same.
Measure both widths at comparable positions, away from rounded corners. Keep front and back measurements separate. A perspective-distorted photograph can change the apparent widths: straighten the view before measuring. The preview is illustrative and does not reproduce a particular card.
One decimal place is a display choice, not proof of measurement accuracy. This calculator does not assign a grade.