The body mass index (BMI) is a measure of relative weight based on an individual’s mass and height.It can approximately calculate the total fat present in the body of a person. In the nineteenth century, a Belgian statistician named Adolphe Quetelet came up with the Quetelet Index of Obesity, which measured obesity by dividing a person’s weight (in kilograms) by the square of his or her height (in inches). While the formula previously called the Quetelet Index for BMI dates to the beginning of the 19th century, the new term “body mass index” for the ratio and its popularity date to a paper published in the July edition of 1972 in the Journal of Chronic Diseases by Ancel Keys, which found the BMI to be the best proxy for body fat percentage among ratios of weight and height. It is a widely used method compared to other body fat detection techniques due to its inexpensiveness and ease of calculating health risks related to obesity.


Nowadays, Body Mass Index (BMI) is calculated manually through measuring tape and weighing scale. There are charts and graphs that show the ratio of proper weight according to height measurement to determine whether a person has too much body fat. This takes time and effort to calculate the body fat.However,automatic calculation of BMI in the context of our country is not so popular and easily accessible to the public except some urban cities.In addition to this,the available automatic BMI calculators aren’t handy enough to move from one place to the other.


The weight and height of the user has been aimed to be measured with the aid of load cell and ultrasonic sensor respectively.However,it can be challenging  for the proponents to calibrate the load cell.The mechanical frame for the placement of the load cell needs to be strong,smooth and of proper shape which can be a challenging task for the proponents to build up.The ultrasonic sensor clamped on the folding stand may not be in the predefined height if mishandled.The  hardware components essential for the project may not be easily available in the local market.If the user doesn’t stand at a proper place on the platform,the ultrasonic waves may not get properly reflected which leads to false calculation of the user’s height  and eventually gives out the wrong BMI value.


The main objective of the project is to design a portable BMI calculator based on micro-controller with notification through buzzer.Likewise the project aims in very accurate measurement of height and weight to avoid BMI calculation errors.

The other objectives of the project are to design a circuit that will combine all the functions of the load cell, ultrasonic sensor and microcontroller; to test and assess the accuracy, reliability and functionality of the device including every parts and components used.


According to wikipedia.org, “The body mass index (BMI) or Quetelet index is a value derived from the mass (weight) and height of an individual.It is defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m2, resulting from mass in kilograms and height in metres.”

According to MedicineNet.com, “BMI is a key index for relating weight to height.It is a person’s weight in kilograms (kg) divided by his or her height in meters squared.”


When the switch is closed,height and weight of the user is automatically detected.For this purpose,the system employs two sensors: load cell and ultrasonic sensor for the measurement of weight and height respectively.The output of the load cell is amplified by the amplifier and is fed to the microcontroller.The ultrasonic sensor mounted on the folding pole is used to measure the distance which is manipulated by the microcontroller to calculate the height of the person.The microcontroller basically inputs these two datas and processes it to calculate the BMI.

Figure 1: Block diagram of the system

    6.1 Weight and Height Sensors

a.Load cell

 Load cell is a sensor that detects force.When force is applied to a load cell, it converts the force into an electrical signal. It can be defined as a weight measurement device necessary for electronic scales that display weights in digits.The load cell for this  project has the capacity of 200kg. The load cell will weigh within the tolerance regardless of the load application point.

Load Cell Bar 0-5kg Force Load Cells | JSumo.com

b. Ultrasonic Sensor

Ultrasonic sensor is an electronic device that emits an acoustic wave beyond the upper range of human hearing (audible range: 20 hertz to 20 kilohertz).

To generate the ultrasonic waves, ultrasonic sensor uses a vibrating device known as a transducer to emit ultrasonic pulses that travel in a cone-shaped beam. The range of an ultrasonic sensor is determined by the frequency of vibration of the transducer.

The Ultrasonic Sensor sends out a high-frequency sound pulse and then times how long it takes for the echo of the sound to reflect back. The sensor has two openings on its front. One opening transmits ultrasonic waves,the other receives them.The speed of sound is approximately 341 meters (1100 feet) per second in air. The ultrasonic sensor uses this information along with the time difference between sending and receiving the sound pulse to determine the distance to an object. It uses the following mathematical equation:

Distance = (Time x Speed of Sound) divided by 2

 where,Time = the time between when an ultrasonic wave is transmitted and when it is received and the distance is divided by 2 because the sound wave has to travel to the object and back.

Ultrasonic Sensor HC-SR04 – NIRT JO


A microcontroller (µC, uC or MCU) is a small computer on a single integrated circuit containing a processor core, memory, and programmable input and output peripherals. It is an integrated circuit that can be programmed to do a specific task and sometimes called as mini computers.By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes.

ATmega328 - 8-bit AVR Microcontrollers


This module uses 24 high precision A/D converter chip HX711. It is a specially designed for the high precision electronic scale design, with two analog input channel, the internal integration of 128 times the programmable gain amplifier. The input circuit can be configured to provide a bridge type pressure bridge (such as pressure, weighing sensor mode), is of high precision, low cost is an ideal sampling front-end module. 

HX711 Module Load Cell Voltage Amplifier Modules | JSumo.com


  • Data accuracy: 24 bit (24 bit A / D converter chip.)
  • Refresh frequency: 10/80 Hz
  • Operating Voltage: 2.7V to 5VDC
  • Operating current: <10 mA
  • Size: 24x16mm

6.4Mechanical design

Figure 6:Microcontroller Based BMI Calculator Mechanical Design

The intended design for the system would be made up of iron and aluminium. The height sensor will be placed on top while the weight sensor at the bottom. The length of the holder of the ultrasonic sensor will be 1.2 ft. The base carrying the load cell is 1.25 ft. long.


The weight of the person is calculated through the load cell or a digital weighing machine.  The height of the person is calculated by the ultrasound sensor.  There is an ultrasounds sensor which both transmits and receives ultrasounds.  First it emits ultrasounds, and when they strike any object or person in its proximity, they are reflected back after striking it, which is sensed by the sensor again. The height is actually calculated by multiplying the ‘speed of the ultrasounds’ and the ‘time taken by the ultrasounds’ to return back to the sensor. The data received from the Ultrasound Sensor and the Load Cell is then sent to the microcontroller, where calculations take place and then the result is sent to the display device.The standard formula for BMI calculation is:

BMI=weight(in kg)/(height in metre)^2



Input weight in kilograms

Input height in meter

Compute BMI=weightl\(height*height)

If BMI<18.5

Print = under weight

Else if BMI<25

print =normal weight

Else if BMI<30

Print = over weight


Print= obessed

End if




The environment to be used for the programming is arduino IDE which is based on C and C++ language.


S.No.Component’s NameQuantityPrice
1.Micro-controller & peripherals1500
2.Load cell12500
3.Platform frame11500
4.Folding stand1500
5.16*4 LCD1450
6.Ultrasonic sensor1350
7.Regulated power supply1250
9.HX711 amplifier1500

Table 1:- List of equipment required with respective price and quantity


The portable BMI calculator will be very helpful  in hospitals,clinics,pharmacies and other health institutions to calculate weight,height and BMI of the patients easily,quickly  and accurately which lessens the job of the health professionals.The obtained informations about the patient help to identify their several health concerns such as malnutrition,overnutrition,etc.It can be of great help in the admission department of the hospitals for faster health care and services. The system will also  help schools and universities when having feeding program for faster distinguishing of unhealthy students. Another help of the design is in fitness clubs and gym halls. Body builders, fitness enthusiasts, and weight lifters need to check their BMI for their target weight according to their height. It can also be used for commercial purposes by installing the device in shopping centres,departmental stores,bus-stops,fun parks,resorts and other social places. The system also finds its application in sports and athletics,military recruitment process,swimming pools,etc. Hence,the system immediately finds its application when it comes to height,weight and BMI measurement.

The project carries  tremendous future scope in every fields and sectors where the measurement of height,weight and BMI are customary. It can replace traditional and existing mechanisms with full user satisfaction in terms of ease,economy,portability,accuracy and robustness.

The research done so far for the project has opened several other doors for the future work .It can be made to count he number of  patients in a hospital creating a database.The details of weight,height and BMI value can be presented to the user in printed form by adding a portable printer.Likewise,we can extend it to suggest a concise  diet plan especially for the underweight and obessed users.The machine can be made to accurately measure children’s BMI by accounting BMI-for-age chart of children.This would need some extra hardware components.

 Body Mass Index for children can’t be calculated accurately as the project doesn’t account BMI-for-age chart of children.Similarly, race/ethnicity and nationality also affect body composition and BMI. Muscular people, athletes and bodybuilders particularly (anybody with a high percentage of muscle mass), have high BMI but can’t be called unhealthy.However,these parameters are neglected in the BMI measurement process.

Recommended For You

About the Author: admin


  1. Magnificent goods from you, man. I have understand your stuff previous to and you’re just
    too great. I really like what you have acquired here, certainly like
    what you’re stating and the way in which you say it. You make it entertaining and you still care for to keep it sensible.

    I can’t wait to read far more from you. This is actually a wonderful site.
    0mniartist asmr

  2. Pingback: tadalafil portugal
  3. Please let me know if you’re looking for a author for your site.
    You have some really great articles and I think I would be
    a good asset. If you ever want to take some of the load off, I’d love
    to write some material for your blog in exchange for a link back to mine.
    Please blast me an email if interested. Thanks!

  4. Today, while I was at work, my cousin stole my iphone
    and tested to see if it can survive a forty foot drop,
    just so she can be a youtube sensation. My apple ipad is
    now destroyed and she has 83 views. I know this is entirely off topic but
    I had to share it with someone!

Comments are closed.