How to calculate LC of micrometer

To calculate the least count (LC) of a micrometer, use the formula: LC = Pitch of screw ÷ Number of divisions on circular scale. The pitch represents the distance the spindle advances in one complete rotation of the thimble, which is typically 0.5 mm for standard micrometers. The circular (thimble) scale is usually divided into 50 equal parts, giving you LC = 0.5 mm ÷ 50 = 0.01 mm.

You can verify the pitch by rotating the thimble from one main scale marking to the next and counting the rotations required—if two complete rotations advance the spindle by 1 mm, the pitch is 0.5 mm. The number of thimble divisions is simply counted around the circumference. Some specialized micrometers have different pitch values (like 1 mm pitch) or different numbers of thimble divisions (like 100 divisions for finer resolution), which would change the least count accordingly. Understanding this calculation helps you verify an unmarked micrometer's precision capability and recognize when you're working with non-standard instruments that might have 0.001 mm least count through additional vernier scales on the thimble sleeve.