In the printing industry, LPI (Lines Per Inch) is the core unit of measurement for printing resolution today; it is also known as “mesh count” or “mesh size.”
Whether used to describe a screen roller (screen roller/sleeve) or a printing plate, LPI refers to the number of screen cells or dots arranged along a length of 1 inch (2.54 cm).
- Anilox roller LPI (Anilox Line Count)
On the screen mesh pattern, LPI determines the density of the surface mesh pits.
Low LPI (e.g., 200–300 LPI): Indicates larger, more sparse mesh openings. This specification typically accommodates a higher ink capacity, making it suitable for large-area full-page prints, white backgrounds, or glossy finishes.
High LPI (e.g., 800–1200+ LPI): Indicates that the dots are extremely small and highly dense. Under the aforementioned 60-degree honeycomb pattern, high LPI allows millions of tiny dots to be packed into a quarter-inch area, making it ideal for printing highly detailed color photographs or fine text.
- Plate LPI (Plate Screen Ruler)
On a printing plate, LPI stands for the density of image dots.
Illustrated magazines, high-end labels, and color boxes typically use printing plates with resolutions of 133 LPI, 150 LPI, or even 175 LPI (the halftone dots are extremely fine, making any graininess invisible to the naked eye).
For rough printing applications such as corrugated cardboard boxes or cement bags, printing plates with a resolution of 55 LPI or 85 LPI may be used (resulting in relatively coarse dots).
- Golden Rule: The configuration relationship between web roller LPI and printing plate LPI
In flexographic printing (Flexo), the LPI of the screen roller must be significantly higher than the LPI of the printing plate; this is known in the industry as the “matching ratio.”
- Traditional Golden Ratio: 4:1 to 6:1
Reason (to prevent dots from falling into the screen): If the smallest dot on the printing plate (e.g., a 1% highlight dot) has a diameter smaller than the opening width of the screen mesh on the screen roller, the dot will directly “fall” into the screen mesh. This can cause the dot to absorb an excessive amount of ink, resulting in Dirty Print, severe Dot Gain, or print smudging during printing.
illustrate:
If your current printing plate is for high-quality color printing at 150 LPI.
When multiplying by 5, you should select a screen mesh size of at least 750 LPI (or higher, e.g., 800–900 LPI) for pairing to ensure perfect printing quality.
- The physical tug-of-war between LPI and BCM (Cell Volume)
During the manufacturing of screen rollers, LPI and BCM are in a mutually constraining relationship:
The higher the LPI value for laser engraving, the smaller the screen mesh size becomes. As the mesh size decreases, the engraving depth cannot be set too deep; otherwise, the ink may become “trapped” inside the screen due to capillary action and fail to be removed during rinsing. Therefore, as the LPI value increases, the maximum Cell Volume (BCM) that the screen roller can achieve is forced to decrease.
| Web roller LPI range | Common BCM combinations | Primary printing applications |
| 200 ~ 350 LPI | 6.0 ~ 12.0 BCM | Full-page layout, large font, opaque background, gloss finish |
| 400 ~ 600 LPI | 3.5 ~ 5.5 BCM | Standard lines, medium-sized text, barcode |
| 700 ~ 900 LPI | 2.0 ~ 3.5 BCM | Detailed lines and four-dot printing on a 133 LPI plate |
| 1000 ~ 1200+ LPI | 1.3 ~ 2.2 BCM | Ultra-high-precision printing with a high-gloss gradient at 150–175 LPI |
International Unit Tip: In Europe and the Chinese mainland, LPI is sometimes not used; instead, the metric unit L/cm (lines per centimeter) is employed.
LPI ÷ 2.54 = L/cm (e.g.: 800 LPI is approximately equal to 315 L/cm)