# Understanding LSB (Least Significant Bit) in Analog-to-Digital Conversion

**URL:** <https://forum.digikey.com/t/understanding-lsb-least-significant-bit-in-analog-to-digital-conversion/59573>\
**Category:** Education\
**Tags:** terminology, engineering-briefs\
**Created:** [August 28, 2025, 6:48am UTC](https://forum.digikey.com/t/understanding-lsb-least-significant-bit-in-analog-to-digital-conversion/59573 "2025-08-28T06:48:18Z")\
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**Post date:** [August 28, 2025, 6:48am UTC](https://forum.digikey.com/t/understanding-lsb-least-significant-bit-in-analog-to-digital-conversion/59573/1 "2025-08-28T06:48:18Z")

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You have heard the term **“LSB” (Least Significant Bit)** many times in electronics. It is often considered in relation to either the **Vref** or the **Full Scale (FS)** of an ADC or DAC, and this can sometimes lead to confusion for readers.

So, this article will help in understanding **the definition of “LSB.”**.

When an ADC ([Analog-to-Digital Converters](https://www.digikey.com/en/products/filter/data-acquisition/analog-to-digital-converters-adc/700?_gl=1*fha2uv*_gcl_dc*R0NMLjE3NTYxMDA4NjcuNGRjNzdkOWFmYmJhMWViOWY3YTIxNTMxMDM0YTY2ZjA.*_gcl_au*MTUwODcxOTg2NS4xNzUyMDYyNTkz)) converts voltage to digital form, one digital code consists of a range of voltage. This voltage range that is equivalent to a single code is called an **LSB ,or least significant bit.**

> **LSB** is the smallest level that an ADC can convert (smallest voltage increment the ADC can detect.), or the smallest increment a DAC can output.

An ADC needs a **voltage reference** to convert an analog signal to digital. Depending on the number of bits it has, it divides the voltage reference into small counts.

* * *

**Example** :  
If this is an **8-bit ADC** , the count will look like 1, 2, 3, … up to 256.

![image](https://global.discourse-cdn.com/digikey/original/3X/3/d/3d2a372a96390efe13096e689b4491401ff2f320.png)

> 1 count is **1 LSB** and is defined as:  
> **LSB** = Vref / 2^N

Where:

- **N** is the number of bits.

> The **Full Scale (FS)** is calculated using the formula:
> 
> - **FS = Vref - 1 × LSB** , or
> - **FS = Vref × ((2^N - 1) / 2^N)**

**Example: Calculate LSB for a -5 to +5 volt input range with a 16bit A/D converter.**  
**FS Range =** 10 Volts (-5V to +5V),  
**16bit resolution** = 65,536 bits  
**LSB** = 10/65536 = 0.0001525 volts/bit (153 µVolts/bit)

#### ADC Conversion Errors Measured in LSB

In ADCs, **conversion errors** are often expressed in terms of **LSB (Least Significant Bit)**.  
If an ADC has a **±2 LSB error** , it means the digital output can deviate by **up to 2 counts** from the ideal value due to internal inaccuracies.

**For example,** if an 8-bit AD converter has 0.0V to 5.0V conversion range and a conversion error of ±2 LSB, the AD conversion range of a 2.5V input,

**LSB** = 5v/ 256 = 0.0195V  
**Ideal digital value for 2.5V input** (AD converter is error-free) = Digital Value= Vin/ LSB  
2.5/ 0.0195 =128⇒0x80 (hex)  
**With ±2 LSB error** , The output could be anywhere from:  
128−2=126⇒0x7E  
128+2=130⇒0x82  
So, the ADC might output 0x7E to 0x82 for a 2.5V input, even though the ideal value is **0x80**.