---
title: "BMI Calculator: Free Online Health & Fitness Tool & FAQs | ShoutingNow"
description: Calculate body mass index with a visual gauge meter, WHO weight status, and supporting stats. Switch US or metric units, then save your result locally.
url: "https://shoutingnow.com/tools/bmi-calculator/"
image: "https://shoutingnow.com/wp-content/uploads/2026/07/shoutingnow-preview-scaled.webp"
---

# BMI Calculator

Enter height and weight to get body mass index, WHO weight status, and a few supporting stats. Switch US or metric units, watch the gauge, and save the result locally if you want to come back to it.

## Using the BMI calculator

Enter height and weight, and this tool estimates body mass index, then places that number in the WHO adult bands. The gauge on the results panel is there so you can see the range at a glance, not because a colorful meter makes the math more “official.” If BMI is new to you, start with [BMI Calculator Explained: What Your Number Really Means](https://shoutingnow.com/blog/bmi-calculator-explained/). That article covers the categories, the health risks people usually ask about, and the cases where the formula misleads.

1. Choose US units or Metric units.
2. Enter age (2 to 120), gender, height, and weight.
3. Click Calculate. The needle moves to your BMI on the meter.
4. Optional: click Save in the result header to keep the calculation in this browser.

## What is BMI?

Body mass index is a simple ratio of weight to height. Clinics and public-health programs use it as a screening check for weight status across large groups. It does not measure body fat on its own. It only tells you whether the combination of height and weight tends to sit in an underweight, normal, overweight, or obesity range. This calculator also shows BMI Prime and the Ponderal Index, two related numbers people sometimes see on the same worksheet.

### BMI table for adults (WHO)

WHO categories for men and women age 20+:

ClassificationBMI (kg/m²)

Severe thinness< 16
Moderate thinness16 to 17
Mild thinness17 to 18.5
Normal18.5 to 25
Overweight25 to 30
Obese Class I30 to 35
Obese Class II35 to 40
Obese Class III> 40

### BMI chart for adults

The chart below plots height against weight with colored WHO bands and dashed contour lines at common BMI values (18.5, 20, 22, 25, and so on). Points above a contour line correspond to higher BMI at that height:

	18.525.030.035.040.0

	150160170180190200406080100120
	Weight (kg)
	Height (cm)
	Adult BMI zones with contour lines

- Underweight < 18.5
- Normal 18.5 to 25
- Overweight 25 to 30
- Obese 30+

	Dashed lines mark BMI values: 18.5, 20, 22, 25, 27, 30, 33, 35, and 40 kg/m².

### Children and teens (ages 2 to 20)

CDC uses BMI-for-age percentiles rather than fixed adult cutoffs:

CategoryPercentile range

Underweight< 5th
Healthy weight5th to 85th
At risk of overweight85th to 95th
Overweight> 95th

Pediatric interpretation depends on age and sex. For children, consult growth charts published by the CDC or your national health authority and discuss results with a pediatric clinician.

### Risks linked to high BMI

A high BMI does not diagnose disease by itself, but the research base behind it is large. People in the higher ranges show up more often with:

- High blood pressure and unfavorable cholesterol profiles
- Type 2 diabetes and insulin resistance
- Coronary heart disease and stroke
- Gallbladder disease and fatty liver
- Osteoarthritis and joint pain
- Sleep apnea and breathing difficulties
- Certain cancers (including breast, colon, kidney, and endometrial)
- Reduced quality of life and higher mortality risk at population level

Staying under 25 kg/m² helps most people’s odds, but what counts as a good target for you is a conversation with a clinician who actually knows your health history, not a number on this page.

### Risks linked to low BMI

The low end of the scale carries its own problems. Being underweight can point to poor nutrition or an illness that has not been caught yet, and it comes with real risks:

- Malnutrition, vitamin deficiencies, and anemia
- Osteoporosis and bone fragility
- Weakened immune function
- Growth or developmental delays in youth
- Reproductive and hormonal disruption in some women
- Greater surgical complication risk when underweight

If you or someone you know is underweight for no clear reason, get it checked out. That is especially true when an eating disorder or a chronic illness could be behind it.

### Limitations of BMI

**In adults:** BMI is a proxy for weight, not a direct read on body fat. Age, sex, ethnicity, muscle mass, and activity level all change what a given number actually means. A sedentary retiree and a muscular athlete can land on the exact same BMI while carrying very different amounts of fat.

- Older adults often carry more fat than younger adults at the same BMI.
- Women typically have higher body fat than men at the same BMI.
- Trained athletes may read as overweight because muscle weighs more than fat.

**In children:** growth spurts and puberty timing shift how a BMI number should be read. It tends to do a better job flagging obesity in kids than catching earlier overweight, since a growth spurt in lean mass can nudge the index up too.

Bottom line: BMI is worth having, but it works best next to waist circumference, activity history, and actual lab work, not on its own.

### BMI formulas

Worked example using a 5′10″ (70 in), 160 lb person, the same defaults as the US tab above:

**US customary units**

**Metric (SI) units**

### BMI Prime

BMI Prime divides your BMI by the upper normal limit (25 kg/m²). It is dimensionless and makes it easy to see how far you sit from the normal ceiling:

ClassificationBMIBMI Prime

Severe thinness< 16< 0.64
Moderate thinness16 to 170.64 to 0.68
Mild thinness17 to 18.50.68 to 0.74
Normal18.5 to 250.74 to 1.0
Overweight25 to 301.0 to 1.2
Obese Class I30 to 351.2 to 1.4
Obese Class II35 to 401.4 to 1.6
Obese Class III> 40> 1.6

## Examples and use cases

### Worked example

Take a 5′10″ (70 in), 160 lb adult, the same numbers used as the US tab defaults:

- BMI comes out to 23.0 kg/m², which sits inside the normal range of 18.5 to 24.9
- For that height, the healthy weight band runs roughly 128 to 174 lb

### Real-world use cases

- Wellness screening: Someone tracks BMI quarterly alongside waist measurement during a structured fitness program.
- Clinical intake: A patient records height and weight before a telehealth visit when the clinic asks for BMI category.
- Athlete context: A rugby player with a lot of muscle mass might get flagged as “overweight” even with low body fat. For someone in that position, the number is one data point to note, not a verdict.

### Ponderal Index

The Ponderal Index cubes height in the denominator instead of squaring it. That can stabilize readings for very tall or short individuals where BMI over- or under-estimates leanness:

**US customary units**

**Metric (SI) units**

## Frequently Asked Questions

### What does the BMI gauge meter show?
It is a semicircle with a needle that swings to your BMI, colored by WHO zone (underweight, normal, overweight, obesity). It is there so you can read your result at a glance instead of squinting at a number.

### What is a healthy BMI for adults?
WHO puts the normal range at 18.5 to 24.9 kg/m² for adults 20 and older. This calculator also translates that into an actual weight range for your height, so you are not doing extra math.

### Can I use pounds and feet?
Yes. Switch to **US units**, then enter your height in feet and inches and your weight in pounds. The tool handles the metric conversion behind the scenes.

### How do I save my BMI calculation?
After you calculate, hit **Save** in the result header. It stays saved locally in this browser on this device, nowhere else.

### Is BMI accurate for athletes?
Not really. Muscle is dense, so it pushes BMI up without adding body fat. If you train hard or carry more muscle than average, treat BMI as one input among several rather than the final word.

### Does this replace medical advice?
No. Think of BMI as a screening number, not a diagnosis. Talk to a clinician before you act on it. Our [BMI explained article](https://shoutingnow.com/blog/bmi-calculator-explained/) goes deeper into where the formula falls short and when to get real medical input.

```json
[{"@context":"https://schema.org","@type":"Organization","name":"ShoutingNow","url":"https://shoutingnow.com/","logo":{"@type":"ImageObject","url":"https://shoutingnow.com/wp-content/themes/shoutingnow-theme/assets/images/logo.png"},"sameAs":["https://x.com/makani20","https://www.linkedin.com/in/makani20/","https://post-see.com"],"contactPoint":{"@type":"ContactPoint","contactType":"customer support","email":"support@shoutingnow.com","url":"https://shoutingnow.com/contact/"},"slogan":"Learn. Build. Grow."},{"@context":"https://schema.org","@type":"WebPage","name":"BMI Calculator","description":"Calculate body mass index with a visual gauge meter, WHO weight status, and supporting stats. Switch US or metric units, then save your result locally.","url":"https://shoutingnow.com/tools/bmi-calculator/","inLanguage":"en-US"},{"@context":"https://schema.org","@type":"SoftwareApplication","name":"BMI Calculator","description":"Calculate body mass index with a visual gauge meter, WHO weight status, and supporting stats. Switch US or metric units, then save your result locally.","applicationCategory":"UtilitiesApplication","operatingSystem":"Web","url":"https://shoutingnow.com/tools/bmi-calculator/","isAccessibleForFree":true,"offers":{"@type":"Offer","price":0,"priceCurrency":"USD","availability":"https://schema.org/InStock","url":"https://shoutingnow.com/tools/bmi-calculator/"},"provider":{"@type":"Organization","name":"ShoutingNow","url":"https://shoutingnow.com/","logo":{"@type":"ImageObject","url":"https://shoutingnow.com/wp-content/themes/shoutingnow-theme/assets/images/logo.png"},"sameAs":["https://x.com/makani20","https://www.linkedin.com/in/makani20/","https://post-see.com"],"contactPoint":{"@type":"ContactPoint","contactType":"customer support","email":"support@shoutingnow.com","url":"https://shoutingnow.com/contact/"}}},{"@context":"https://schema.org","@type":"HowTo","name":"How to use BMI Calculator","description":"Calculate body mass index with a visual gauge meter, WHO weight status, and supporting stats. Switch US or metric units, then save your result locally.","url":"https://shoutingnow.com/tools/bmi-calculator/","inLanguage":"en-US","step":[{"@type":"HowToStep","name":"US units","text":"Choose US units or Metric units."},{"@type":"HowToStep","name":"Enter age (2 to 120), gender, height, and weight.","text":"Enter age (2 to 120), gender, height, and weight."},{"@type":"HowToStep","name":"Calculate","text":"Click Calculate. The needle moves to your BMI on the meter."},{"@type":"HowToStep","name":"Save","text":"Optional: click Save in the result header to keep the calculation in this browser."}]},{"@context":"https://schema.org","@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What does the BMI gauge meter show?","acceptedAnswer":{"@type":"Answer","text":"It is a semicircle with a needle that swings to your BMI, colored by WHO zone (underweight, normal, overweight, obesity). It is there so you can read your result at a glance instead of squinting at a number."}},{"@type":"Question","name":"What is a healthy BMI for adults?","acceptedAnswer":{"@type":"Answer","text":"WHO puts the normal range at 18.5 to 24.9 kg/m² for adults 20 and older. This calculator also translates that into an actual weight range for your height, so you are not doing extra math."}},{"@type":"Question","name":"Can I use pounds and feet?","acceptedAnswer":{"@type":"Answer","text":"Yes. Switch to US units, then enter your height in feet and inches and your weight in pounds. The tool handles the metric conversion behind the scenes."}},{"@type":"Question","name":"How do I save my BMI calculation?","acceptedAnswer":{"@type":"Answer","text":"After you calculate, hit Save in the result header. It stays saved locally in this browser on this device, nowhere else."}},{"@type":"Question","name":"Is BMI accurate for athletes?","acceptedAnswer":{"@type":"Answer","text":"Not really. Muscle is dense, so it pushes BMI up without adding body fat. If you train hard or carry more muscle than average, treat BMI as one input among several rather than the final word."}},{"@type":"Question","name":"Does this replace medical advice?","acceptedAnswer":{"@type":"Answer","text":"No. Think of BMI as a screening number, not a diagnosis. Talk to a clinician before you act on it. Our BMI explained article goes deeper into where the formula falls short and when to get real medical input."}}]},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"ShoutingNow","item":"https://shoutingnow.com/"},{"@type":"ListItem","position":2,"name":"Tools","item":"https://shoutingnow.com/tools/"},{"@type":"ListItem","position":3,"name":"BMI Calculator","item":"https://shoutingnow.com/tools/bmi-calculator/"}]}]
```