To convert 138 millimeter to inch, multiply by the conversion factor 0.039370. 138 millimeter multiplied by 0.039370 equals 5.43306 inch, which rounds to 5.4331 inch.

138 millimeter equals exactly 5.433071 inch. For practical purposes, this is often rounded to 5.4331 inch.

Objects measuring approximately 138 millimeter include the diagonal screen of an iPhone 13 mini (137.16 mm), the length of a standard compact TV remote control, and the width of a specific pocket-sized planner.

Converting millimeter to inch is useful for international collaboration in engineering, manufacturing, and design, especially when working with countries primarily using the Imperial system like the United States. It ensures compatibility and precision in specifications across different regional standards.

For quick estimation, remember that 1 millimeter is roughly 0.04 inch, so 138 mm is about 138 x 0.04 = 5.52 inches. For precision, always use a calculator with the 0.039370 conversion factor. A visual aid is to think of a 5.4-inch smartphone screen, which is approximately 138 millimeter diagonally.