A smart scale measures body fat with bioelectrical impedance analysis (BIA): it sends a tiny electrical current through your body and measures how strongly the tissue resists it. A review in Nutrition Journal puts the usual signal at about 800 microamps and 50 kHz. Water-rich lean tissue conducts that current easily, while fat resists it. The scale turns the resistance, plus your height, age and sex, into an estimated body fat percentage.
That percentage is an estimate. Smart scales weigh you to within a few hundred grams, but their body fat figures can be several kilograms out. The trend over weeks tells you more than any single reading.
What happens when you step on a smart scale
A smart scale is two instruments in one: a digital weighing scale and an impedance meter. On a scale with metal pads, a weigh-in runs in this order:
- Sensors under the glass weigh you, the same way an ordinary digital bathroom scale does.
- Once the weight locks, the metal pads pass a small alternating current up one leg and down the other.
- The scale measures impedance, the opposition your body puts up to that current.
- Software combines the impedance with your weight, height, age and sex to estimate fat-free mass. Fat mass is your weight minus that fat-free mass.
- The app works out the rest from those two numbers: body fat percentage, muscle, body water, bone mass, visceral fat and BMR.
Step 4 is a prediction equation. A 2021 study in JMIR mHealth and uHealth describes the usual model as body impedance, height, weight and age, trained against DEXA scans. Each brand builds its own equation, which is why two scales rarely agree on body fat even when they agree on weight.
The current needs bare skin. Socks block it, so scales with metal pads ask you to stand barefoot. Omace's instructions for its Hoffen scales with pads also ask you to stay on for a few seconds after the weight locks. In that time the body readings are worked out and sent to the app.
Why your height, age and sex change the result
A smart scale cannot see how tall or how old you are. It takes those details from the profile you set up in the app, and the equation leans on them heavily. If the profile height is wrong, every morning's estimate starts from the wrong body size. Omace's product guides suggest measuring your height on a stadiometer if you are not sure of it, and the guide on how to measure height accurately covers the method.
Population matters too. The Nutrition Journal review notes that BIA equations validated for one ethnic group may not hold for another. It also reports that Asian populations, Singaporean Indians among them, carry a higher body fat percentage at the same BMI than Europeans.
Some smart scales skip impedance altogether. The Venus EPS-6399 App and Hoffen HO-9 App have no metal pads, so their apps estimate body fat and the other values from your weight, height, age and gender alone. Socks are fine on these two. Their body fat figure is a formula result: useful for following a trend, but no current passes through your feet.
Foot pads, hand grips and what they measure
Where the electrodes sit decides which part of the body the current crosses. On a foot-to-foot scale, impedance is measured through the legs and lower trunk only. Devices that add hand electrodes also take in the arms and upper trunk, according to a 2008 study in Obesity Facts.
That study compared consumer BIA devices with DXA scans in 106 adults. For body fat percentage, the 95% limits of agreement were −6.6 to +4.6 points for the hand-and-foot device. They widened to as much as −14.5 to +8.6 points for the foot-to-foot devices. The authors recommend hand-and-foot designs for individual use and foot-to-foot scales for group estimates in field studies.
- Metal pads under the feet: the Hoffen HO-18 App, HO-19 App, HO-36 App and HO-45 App. You stand barefoot on the pads.
- Hand grips: Omace's ultrasonic height and weight machine reads body composition through two hand grips, so users can keep their shoes on. Its ultrasonic sensor also measures height without contact, from 80 to 200 cm.
- No electrodes: the Venus EPS-6399 App and Hoffen HO-9 App, which estimate body values from your profile.
How accurate smart scale body fat readings are
Smart scales are accurate for weight and rough for body fat. The JMIR study tested three consumer smart scales against DEXA in hospital patients. Median weight errors were between 0 and 0.3 kg. Fat mass came out lower than DEXA by a median of 2.2 to 4.4 kg, and the authors concluded that smart scales should not replace DEXA in patient care.
The Nutrition Journal review reaches a similar view: BIA measures body fat accurately in controlled clinical conditions, but its performance outside them is inconsistent. For a home user, the practical rule follows from both studies. Compare readings from the same scale, taken the same way, and judge the direction over several weeks. Omace's calibration guide answers are smart scales accurate separately for weight and for body fat.
What makes the reading change from day to day
Body water drives most day-to-day swings, because the current travels through water and electrolytes. The Nutrition Journal review lists three effects worth knowing:
- Dehydration can raise resistance by about 40 ohms, enough to underestimate fat-free mass by 5 kg.
- A heavy meal raised impedance when measured one hour after eating.
- Moderate or hard exercise warms the muscles and skin and lowers impedance, so the review advises against measuring within several hours of a workout.
Skin matters as well. Omace's instructions note that dry feet work best, and that wet or very dry skin can change the body fat reading. A steady routine removes most of the noise:
- Weigh at the same time each day, best in the morning before eating.
- Keep the scale on a hard, flat floor such as tile or stone, never on a carpet or mat.
- Stand barefoot with dry feet on the metal pads, and stay still until the reading finishes.
- Skip the weigh-in straight after a workout or a large meal.
- Compare readings on one scale only, because each brand uses its own equation.
What each number on the app means
Only one number from a smart scale is measured directly: your weight. Everything else is calculated from weight, impedance and your profile.
| Number | What it is | How to read it |
|---|---|---|
| BMI | Weight in kg divided by height in metres squared | Calculated from weight and profile height; no current needed |
| Body fat % | Share of your weight that is fat | Estimate; follow the weekly trend |
| Muscle mass and protein | Parts of your fat-free mass | Estimate from the same equation |
| Body water | Water as a share of body weight | Moves with drinking, food and exercise |
| Visceral fat | A rating for fat around the organs | Estimate; cross-check with a waist tape |
| BMR and body age | Energy used at rest, and an age score | Calculated from the other numbers |
The World Health Organization calculates BMI as weight in kilograms divided by height in metres squared. WHO defines adult overweight as a BMI of 25 or more and obesity as 30 or more. A consensus of Indian experts uses lower cut-offs: a review in Nutrients describes a consensus for Asian Indians of 23–24.9 for overweight and 25 or more for obesity. You can check your own figure on Omace's BMI calculator.
A waist tape is a useful cross-check for the visceral fat rating. The same review gives the Asian Indian consensus cut-offs for abdominal obesity as a waist of 90 cm or more in men and 80 cm or more in women.
Weight and body fat can also move in opposite directions. Your weight can stay the same while body fat falls and muscle rises, a change a weight-only scale cannot show.
Omace smart scales and how each gets its numbers
Omace sells six smart body scales and one clinic machine with body composition. The table lists all six scales and the clinic machine, with prices from the Omace store (October 2026).
| Model | How body fat is worked out | Body values | App | Price |
|---|---|---|---|---|
| Venus EPS-6399 App | Estimated from weight and profile, no pads | 25 | Omace Fit | ₹699 |
| Hoffen HO-9 App | Estimated from weight and profile, no pads | 25+ | My Fit India | ₹699 |
| Hoffen HO-18 App | BIA, 4 foot electrodes | 15+ | FitDays | ₹799 |
| Hoffen HO-19 App | BIA, 4 foot electrodes | 14 | FitDays | ₹899 |
| Hoffen HO-36 App | BIA, 4 foot electrodes | 14 | FitDays | ₹1,499 |
| Hoffen HO-45 App | BIA, 4 foot electrodes, plus heart rate | 16 | FitDays | ₹2,499 |
| Ultrasonic height and weight machine | BIA through 2 hand grips | 18 | AiLink | ₹16,999 |
The Hoffen HO-18 weight machine with app is the lowest-priced Omace model with metal pads. It reads 15+ body values through 4 electrodes and sends them to the free FitDays app.
The Hoffen HO-45 body composition scale is the only bathroom-style model whose colour screen shows body fat, BMI and heart rate without a phone. It reads heart rate through the same four metal pads in about 15 seconds and weighs in 50 g steps. The Hoffen HO-36 body fat analyzer sends 14 values to the FitDays app and shows your weight, also in 50 g steps, on a colour VA screen. The Venus EPS-6399 body fat weighing machine is made in India and sends your weight to the free Omace Fit app, which estimates 25 metrics from your profile.
Family use depends on the app. FitDays allows up to 24 profiles, My Fit India allows as many as you like, and on Omace Fit each person adds their own profile. Omace Fit syncs your readings with Google Fit; it does not sync with Apple Health yet. The full range is listed under smart weighing scale, and the Omace Fit app guide covers set-up and pairing.
Who should use weight-only mode
BIA is not suitable for everyone. Omace's instructions for its scales with metal pads cover two groups. People with a pacemaker or other implanted electronic device, and pregnant women, should not use the body fat mode. Using the scale for weight only is fine. Every Omace smart scale still shows your weight on its own display without the app.
No smart scale diagnoses anything. Body fat, visceral fat and body age are estimates for tracking, and a doctor should look at any health concern, if needed with a clinical method such as DEXA.
Omace Brands Private Limited has made and supplied weighing scales in India since 1994, from Bagru, Jaipur. Its smart body scales are made in India and checked before dispatch. Scales bought from the Omace store carry a 2-year warranty on manufacturing defects and are delivered across India. More about Omace. As a manufacturer, Omace Brands Private Limited holds ISO 9001:2015, ISO 13485:2016 and EU MDR quality certificates, and CE and US FDA compliance certificates; each is listed with its certificate number on the Omace certificates page.
