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  1. Glossary
  2. /Physics
  3. /Least Count

What is Least Count?

In short

The least count of a measuring instrument is the smallest value it can measure reliably. It is the difference between two neighbouring marks on its scale.

In simple words

A metre rule has a least count of 1 mm1\ \text{mm}1 mm. A vernier caliper has a least count of value of one main scale divisionnumber of divisions on the vernier\dfrac{\text{value of one main scale division}}{\text{number of divisions on the vernier}}number of divisions on the verniervalue of one main scale division​, commonly 0.1 mm0.1\ \text{mm}0.1 mm. A screw gauge has a least count of pitchnumber of divisions on the circular scale\dfrac{\text{pitch}}{\text{number of divisions on the circular scale}}number of divisions on the circular scalepitch​, commonly 0.01 mm0.01\ \text{mm}0.01 mm. A smaller least count gives a more precise reading.

Example

A screw gauge has a pitch of 0.5 mm0.5\ \text{mm}0.5 mm and 505050 divisions on the circular scale. Its least count is 0.5 mm50=0.01 mm\dfrac{0.5\ \text{mm}}{50} = 0.01\ \text{mm}500.5 mm​=0.01 mm.

Also searched as: least count of vernier caliper and screw gauge.

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Related terms

  • Errors in Measurement

← All glossary terms

Learn it in

  1. Measurement, Units and the SI SystemClass 11 to 12
  2. Accuracy, Errors and Significant FiguresClass 11 to 12
  3. Dimensions and Dimensional AnalysisClass 11 to 12
All lessons on this topic →

Practise

  1. A student says: "I can find s = ut + 1/2at² by dimensions alone." Explain why not, and…Medium
  2. In SI units G = 6.67 × 10⁻¹¹ N m² kg⁻², with dimensions [M⁻¹ L³ T⁻²]…
Medium
  • The speed v of a wave on a stretched string depends on the tension F and the mass per…Hard
  • The period T of a pendulum might depend on the bob's mass m, the length l and g…Hard
    • All problems on this topic →

    Quick questions

    1. Why can dimensional analysis **not** derive s = ut + 1/2at²?Medium
    2. Which of these quantities has **no** dimensions?Easy
    3. The distance covered by a cyclist is given as s = a + bt + ct², with s in metres and t…Medium

    More Physics terms

    1. Acceleration
    2. Acceleration Due to Gravity (g)
    3. Adiabatic Process
    4. Amplitude
    5. Angle of Incidence
    6. Angle of Reflection
    All Physics terms →

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