How it works:

BMI, or Body Mass Index, is a simple calculation used  to assess if a person has a healthy body weight  for a given height.

It's calculated using the following formula:

BMI = (Weight/Height2)*703

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BMI is often used to categorize weight status:

Underweight: BMI less than 18.5
Normal weight: BMI 18.5–24.9
Overweight: BMI 25–29.9
Obesity: BMI 30 or more

What health risks
every BMI category brings

Your Body Mass Index: NN

Severe Thinness

BMI < 16

High risk of severe nutritional deficiencies, weakened immunity, muscle loss, and osteoporosis. Individuals may experience extreme fatigue, anemia, and hormonal imbalances, affecting fertility.

Moderate Thinness

BMI 16 - 17

Moderate risk of nutritional deficiencies, immune weakness, and fatigue. Bone density may be reduced, and there is a mild increase in susceptibility to infections.

Mild Thinness

BMI 17 - 18.5

Some risk of nutritional deficits, slight immunity reduction, and mild fatigue. Potential fertility issues may occur, but risks are generally low.

Normal

BMI 18.5 - 25

Associated with the lowest health risks and balanced well-being. With a healthy diet and regular activity, this range promotes optimal mental and physical health.

Overweight

BMI 25 - 30

Increased risk of heart disease, type 2 diabetes, and joint strain. There may also be a higher likelihood of sleep apnea and fatty liver disease.

Obese Class I

BMI 30 - 35

Moderate risk for cardiovascular disease, type 2 diabetes, and joint issues. Elevated risks for sleep apnea, fatty liver, and gallstones.

Obese Class II

BMI 35 - 40

High risk of heart disease, diabetes, mobility problems, and certain cancers. Individuals are more likely to experience severe joint pain, respiratory issues, and reduced mobility.

Obese Class III

BMI > 40

Extremely high risk of life-threatening conditions, including heart disease, severe diabetes, respiratory issues, and certain cancers. Life expectancy is significantly reduced due to complications associated with extreme obesity.

Why it's important to know your BMI

Knowing your BMI is important because it provides a quick and accessible assessment of your body weight relative to your height, which can help indicate potential health risks associated with being underweight, overweight, or obese. Here’s why BMI matters:

Setting Health
and Fitness Goals

Knowing your BMI helps in setting realistic health and fitness goals. For individuals looking to maintain or change their body composition, BMI can serve as a general benchmark.

It is a useful starting point for determining  if further assessments are needed, such  as measuring body fat percentage, which provides more detailed insights into body composition.

Identifying Health Risks

BMI can help identify risks of conditions like heart disease, stroke, high blood pressure, type 2 diabetes, and certain cancers. People with higher BMIs, particularly over 30,  often have an increased likelihood of developing these issues.

Being underweight (BMI under 18.5) also poses risks, including nutritional deficiencies, weakened immune function,  and potential osteoporosis due to low bone density.

Tracking Weight Changes Over Time

Regularly monitoring BMI allows individuals to track changes over time, whether they are managing weight loss, weight gain, or maintaining a healthy weight.

For healthcare providers, BMI trends in patients can signal lifestyle, dietary, or health adjustments that might  be necessary for long-term wellness.

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Learn more about your BMI
and how to improve
it in our newsletter.

Why BMI  is not enough  for your Fitness Journey?

Body Mass Index (BMI) is a simple calculation based

on height and weight and has serious limitations — especially if you're serious about fitness.

It Doesn’t Differentiate Between Muscle and Fat

BMI treats all weight the same. That means a muscular athlete and someone with a higher body fat percentage could have the same BMI—even though their bodies are completely different.

It Ignores Body Composition

Reaching fitness goals usually involves improving body composition—meaning the ratio of fat to muscle. BMI doesn't account for that.

It Doesn’t Reflect Fitness
or Strength

You could have a "normal" BMI and still have low endurance, poor mobility, or weak muscles. Likewise, someone with a "high" BMI might be able to lift heavy, run fast, and have a healthy heart. Fitness is about performance and health, not just numbers.

It Doesn’t Consider Individual Differences

Everyone’s body is different. Genetics, bone density, sex, and even age can influence weight and body structure. BMI paints with a broad brush, missing the nuances that matter when you’re working toward specific fitness or aesthetic goals.

How the AURA Strap 2 can help

The AURA Strap 2 gives you a complete picture of your body composition—right from your Apple Watch.

With just a 30-second scan, AURA Strap 2 syncs data directly to your Apple Health and AURA App, helping you track progress and adjust your fitness or nutrition plan in real time.

Why It Matters:

Traditional metrics like weight and BMI don’t tell the full story. AURA Strap 2 helps you track what actually changes when you train—your body composition, water levels, and muscle development. Whether you're bulking, cutting, or losing weight, you'll get insights that move you forward.

What AURA Strap 2 Tracks:

Body Fat %

Monitor fat loss, not just weight loss

Muscle Mass

See how your strength training is paying off

Water Levels

Stay balanced and avoid underperformance

Lean Mass

Fine-tune your body’s fuel and function

AURA Strap 2

$159.00

Color

Coal Black

Summer Gray

Navy Blue

Crimson Red

Apple Watch Size

42mm (41/40/38mm)

46/49mm (45/44/42mm)

Quantity

Key features

Cutting-Edge Precision

Accuracy to 95% in comparison with the golden standard DEXA-scan

Real-Time Data

Monitor your body composition

anytime anywhere

Long Battery Life

Up to 6 months on a single battery

Splash Resistant

AURA Strap 2 is sweat resistant and safe to use in shallow water

Full sync with HealthKit

AURA App is fully compatible  with Apple HealthKit

Comfort and Durability

Experience superior comfort and durability with device ergonomic design and premium materials

FAQ

What does it do?

AURA Strap 2 measures your body composition and hydration level on your Apple Watch.

Does it work with my Apple Watch?

Supports Apple Watch Series 3 to Series 10, including SE and Ultra 2. It connects with 38/40/41/42 and 42/44/45/46/49 mm Watches. Choose the size to fit your Watch.

How can body composition tracking help me?

A series of day-by-day measurements shows the trends as your body composition changes. It makes your workouts more efficient, because you can understand (by the numbers) what exercises are definitely good or bad for you.

Does it measure hydration?

AURA Strap 2 measures how much water you have in your body with the help of bioimpedance analysis.

Does AURA Strap 2 fit my wrist?

Each device comes with 4 sets of Infinite loops. The set for 38/40/41mm Apple Watches includes XS, S, M, and L loop sizes and fits 130–200mm wrists. The set for 42/44/45/49mm Apple Watches includes M, L, XL, and XXL loop sizes and fits 140–220mm wrists. You can pick the size and tightness according to your preferences!

Can I share AURA Strap 2 with a friend or family member?

AURA Strap 2 measures your body composition and hydration level on your Apple Watch.

Is it waterproof?

AURA Strap 2 is water resistant. The device will not be affected by high moisture or immersion in water up to 50cm / 20 inches. But the device may suffer from direct exposure to a high-pressure water stream. We do not recommend diving, water skiing, or other activities involving high-velocity water or submersion below shallow depth.

How are AURA Strap 2’s electrodes made?

The electrodes on each side of the device are made using medical stainless steel (contains nickel).

How long does it work on a single charge?

AURA Strap 2 works for up to 6 months using a standard, replaceable round coin battery (CR1632). Simply change spent batteries with the included pick, and it's ready to use.

Is it safe to use AURA Strap 2 with a pacemaker?

No, we don't recommend using the device with a pacemaker.

Can the AURA Strap 2 detect medical conditions or illnesses?

No, the AURA Strap 2 is not designed to detect or treat any medical conditions or illnesses.

How does Strap 2 connect with Apple Watch? Is it secure?

Strap 2 uses a BLE 4.2+ interface to transfer measurement data. Data transferred between devices is encrypted. The reliability of Bluetooth reduces the number of unsuccessful measurements by 99.99% and allows users to take measurements in any environment.