Why Most BMI Calculation Methods Are Wrong (And How to Fix Them)
Most people calculate their BMI number, but still, they feel confused about whether it is right or not. What if your BMI formula is right, but your calculation method is wrong? Even small mistakes in measuring height and weight can change your BMI results.
So here you can learn how to calculate BMI manually and see unit conversion rules like kg, meters, and inches. That seems like a very small issue, but it creates a big problem.
Moreover, it also clear the concept of the online BMI calculator result as well.
How do you calculate BMI manually (Step-by-Step Guide)?
Let’s start with these 3 steps given below to calculate BMI manually, and then we will discuss our online BMI calculator results, and then we will compare it with manual calculations.
Step 1. Measure Your Weight Correctly
Your BMI results highly depend on this step. It is just because a small mistake in measuring your current weight, which makes your BMI wrong. Always make sure to measure weight on a clear surface, and not to wear shoes and heavy jackets, etc. That increases your weight, and that’s why the BMI value will increase.
Step 2. Measure Your Height without Errors
Height plays a major role in BMI calculations. But most people ignore this step and do not measure height accurately, that make BMI wrong. A correct method to measure height is by standing straight without shoes because the height of shoes is included as well, and then your overall measurements become wrong.
Apply the BMI Formula
The main step for BMI calculations is this. For this, first, you have to know the real formula for BMI calculations. This is not a complex formula, but most of the time it is used incorrectly and gives wrong values.
Below is the basic BMI formula for everyone according to the basic BMI standard.
BMI = Weight (kg) ÷ Height (m²)
For example, if your weight = 60 kg and your height = 1.7 meters (5.5 feet), then your BMI = 20.8. And your weight category is healthy.
Here you also get information on weight categories according to your BMI.
BMI Formula (Simple & Accurate)
Use this formula to calculate your Body Mass Index correctly
BMI = Weight (kg) ÷ Height (m²)
Example:
Weight = 60 kg
Height = 1.7 m
BMI = 60 ÷ (1.7 × 1.7) = 20.8
⚠️ Always use the same unit system. Mixing feet with kilograms can change your result.
How to Calculate BMI in Different Units (KG, Feet & Inches)
Most of the confusion that everyone searches for is this. It’s just because most people don’t know correctly which units have to be used in the BMI formula.
Here’s the solution to this problem in simple language.
BMI Calculation in Metric Units (kg & meters)
This is a fact that no one wants to do conversions. So, this is the most useful and straight forward way to calculate BMI because it uses standard units, and it does not need to do any conversions. This only needs weight in kilograms and height in meters. So, if you want to avoid conversion problems, use standard units in calculations.
BMI Calculation Using KG/Pounds & Feet/Inches
This is also a fact that most people know their height in feet and inches. Now the problem is generated because the formula needs height in meters, and you know it in feet. So you need to do conversions before putting it in the formula. And here, 1 foot = 0.3048 meters, you have to calculate according to this and measure height.
Some people know their weight in pounds, so for that you also need to do a little conversions. And here, 1 Pound = 0.4536 kg, you have to calculate according to this to measure weight.
After a complete conversion, finally put the final value into the formula and get your BMI accordingly.
Example: BMI Calculation Using KG/Pounds & Feet/Inches
This example shows how to calculate BMI correctly when height is measured in feet and inches.
Weight: 70 kg (154 Pounds)
Height: 5 feet 7 inches
Step 1: Convert height into meters
5 feet 7 inches ≈ 1.70 meters
Step 2: Apply the BMI formula
BMI = 70 ÷ (1.70 × 1.70) = 24.2
⚠️ Always convert height into meters before calculation. Skipping this step can lead to incorrect BMI results.
Here’s a general table for Height Conversion (Feet & Inches to Meters)
Height Conversion Table (Feet & Inches to Meters)
Use this table to convert your height into meters before calculating BMI.
| Height (Feet & Inches) | Height (Meters) |
|---|---|
| 5’0″ | 1.52 m |
| 5’3″ | 1.60 m |
| 5’5″ | 1.65 m |
| 5’7″ | 1.70 m |
| 5’9″ | 1.75 m |
| 6’0″ | 1.83 m |
✔ Accurate height conversion helps avoid BMI calculation mistakes.
BMI Online Calculators vs Manual Calculation (Pros & Cons)
As everyone knows, Online calculators reduce human errors in calculation. So it is useful for us to compare our results with online calculators.
By comparing our calculations,
1. You can see your mistakes, and moreover, you can also check your health categories accordingly.
2. It also saves your time in conversions and calculations.
Our BMI Calculator Tool helps you to get accurate results and save your time in doing conversions and calculating it according to WORLD HEALTH ORGANIZATION (WHO) standards, and tells your weight category according to your health conditions.
Here’s the table for Manual vs Online BMI calculations Comparison
Manual vs Online BMI Calculation
A clear comparison to help you choose the right BMI calculation method.
| Feature | Manual Calculation | Online Calculator |
|---|---|---|
| Accuracy | Accurate when formula & units are applied correctly | Accurate if inputs are entered properly |
| Ease of Use | Requires Calculations Effort and is slow | Very Fast and easy |
| Unit Conversions | Must be done manually | Automatically handled |
| Understanding BMI | Helps you understand how BMI actually works | Shows the result without explaining the logic |
| Best For | Learning, education, and accuracy checks | Quick checks and regular tracking |
💡 Tip: Use manual calculation to understand BMI, and online tools to save time.
✔ Both methods are useful—accuracy depends on how carefully you use them.
Benefits of Using an Online BMI Calculator
Here are some benefits of using an online BMI calculator to calculate BMI.
1. An online BMI calculator reduces the errors that a normal person like us would not realize.
2. It saves your time for conversions and calculates it faster than manual calculation.
3. It allows you to check your BMI daily, which helps you in your daily progress.
4. It tells you about your weight category, like overweight, underweight, and healthy, according to your BMI number.
5. The Online BMI Calculator calculates BMI on the WORLD HEALTH ORGANIZATION (WHO) Standard.
Limitations of BMI Calculators
As this is a fact, everything has some features and limitations as well.
Some of the disadvantages of the BMI calculators are described below, which tell you some issues with these BMI calculators.
1. Firstly, it gives you a display of your health, but it does not describe your full body story.
2. The BMI calculator cannot differentiate between body muscle mass and body fat, and can only describe according to the weight we give it.
3. It also ignores different factors on which BMI matters, like age, gender, and ethnicity.
When Manual BMI Calculation is Better
Calculating BMI on your own also has some benefits as well, but only using a tool is not good as well. So here are some benefits of manual calculations.
1. It gives you full control of your own calculations, and you are clear with your results.
2. Online calculators seem to be very accurate, but sometimes they also give some bugs while calculating due to a glitch, but manual calculations contain no technical bugs or glitches.
3. If you calculate BMI manually, and then you check it with the online calculator, and if both are the same, you build trust with that BMI tool calculator site.
Conclusion
Calculating BMI on your own is not difficult. But the main thing is that you need the right method for calculating it. You need to remember units and conversions, etc. While, online calculators save your time in conversions and quick calculations.
But remember, BMI is the initial point for your health improvement. Use this to check your weight category, and then you will combine it with your daily lifestyle changes and improve your daily routine accordingly.
You can also get here the latest updates on BMI.
FAQS
1. Which basic information is needed in BMI calculations?
You only need to put your weight and height to calculate BMI.
2. What is BMI, and how to calculate BMI?
BMI is a basic health screening tool for everyone. For more BMI guidance, visit our BMI Basic Guide content. And, now you can automatically calculate your BMI with any BMI Calculator that works according to the WORLD HEALTH ORGANIZATION (WHO) standard.
3. What is the correct BMI formula?
The BMI formula is simple and easy; you can divide your weight by the square of your height.
BMI = Weight (kg) ÷ Height (m²)
4. Why do most people calculate BMI incorrectly?
There are some reasons below that cause people to calculate BMI incorrectly:
1. They make mistakes in measuring height and weight.
2. They use a different unit system in calculations and do not focus on proper conversions.
3. They do not use an accurate formula to calculate BMI.
5. Is manual BMI calculation is more better than online calculations?
Well, that’s a very confusing question. But the answer is that, if you calculate BMI correctly on your own, then manual calculations are better, but online calculators do fast calculations and save your time as well.
6. Can BMI be calculated by using feet and inches?
Yes, you can calculate BMI by using feet and inches, but you have to do conversions before putting it in the tool. But Great news is that our BMI calculator has an option to automatically convert your units according to your choice.
7. Which BMI system is easier to use?
The basic standard unit for BMI calculations, kilograms and meters, is an easier unit to calculate BMI because it avoids to do any conversion.
8. Do online BMI calculators give correct results?
Yes, if you put the correct height and weight, you will get the correct BMI value faster than manual calculations.
9. What are the limitations of using online BMI calculators?
Online BMI calculators do not differentiate between muscle mass and body fat, and it does not focus on the age, gender, etc. of any person.
10. Can BMI do impact on our daily lifestyle?
Yes, daily check of BMI impact on our daily lifestyle, and it affects on our health as well.
You can also check our blog on the impact of BMI on our daily lifestyle.
