On-center size in cabinet hardware refers to the measurement between the centers of two adjacent mounting holes on a piece of hardware, such as handles, knobs, or pulls used on cabinets, drawers, or furniture. This measurement is essential when replacing or installing new hardware to ensure proper fit and alignment.

To determine the center-to-center measurement, you must measure the distance between the centers of the two mounting holes.

For example, if you have a cabinet handle with two mounting holes, you would measure the distance between the centers of those holes.

When purchasing new cabinet hardware, it's critical to match the center-to-center measurement of the new hardware to the existing holes or intended installation location. This ensures that the new hardware will line up correctly with the pre-drilled holes or allows you to drill new holes with proper spacing.

Center to center size is usually expressed in inches or millimeters. Common measurements include 3 inches (76mm), 3.75 inches (96mm), 4 inches (102mm), and 5 inches (128mm), though other sizes are also available. It's important to note that center-to-center sizing can vary between different manufacturers and styles of hardware, so it's essential to double check your measurements before purchasing.

By understanding the center-to-center size of your cabinet hardware, you can ensure a proper fit and achieve a cohesive look when replacing or installing new hardware in your cabinets or furniture.