This guide explains what each type actually measures, where a professional analyser fits in, who needs which, and a short buying checklist. If you want the accuracy evidence for home scales, that is in our separate guide on whether smart body-fat scales are accurate<\/a>.<\/p>\n BMI, or body mass index, is weight in kilograms divided by height in metres squared. A person who weighs 70 kg and is 1.70 m tall has a BMI of 70 \u00f7 (1.70 \u00d7 1.70), which is about 24.2.<\/p>\n So the only thing a “BMI machine” measures is your weight<\/strong>. Height comes from you, typed into the scale or its app. The BMI number is arithmetic you could do on a phone calculator. That is not a criticism. Weight is genuinely useful, and a good scale measures it well. But a BMI scale cannot tell you what the weight is made of.<\/p>\n For Indians the BMI cut-offs are also lower than the international ones. A WHO expert consultation in 2004<\/a> found that many Asian populations have a high risk of type 2 diabetes and heart disease below a BMI of 25, and proposed public-health action points at 23 and 27.5. Indian criteria, restated in the 2025 revised definition of obesity for Asian Indians<\/a>, treat 23 to 24.9 as overweight and 25 or more as obesity. Scale apps do not always say which bands they use, so read your BMI against 23 and 25 yourself.<\/p>\n BMI cannot separate muscle from fat. UK guidance from NICE (NG246<\/a>) tells clinicians to interpret BMI with caution in people with high muscle mass, and in people aged 65 and over. It also notes that a person in the healthy BMI range may still carry excess fat around the middle.<\/p>\n Two everyday Indian examples show why that matters:<\/p>\n If you only want to track weight, a basic scale is fine. If you want to know whether you are losing fat or muscle, BMI cannot tell you.<\/p>\n A body composition scale, often sold as a smart scale or a “weight machine with fat analysis”, uses bioelectrical impedance analysis (BIA)<\/a>. Lean tissue holds a lot of water and conducts current well; fat holds little water and resists it. The scale measures that resistance and uses an equation to estimate fat, muscle and water.<\/p>\n What makes one body composition scale different from another:<\/p>\n Hydration matters for every BIA device. The ESPEN clinical guideline on BIA<\/a> notes that it works well in healthy people with stable fluid balance, and that results in people with abnormal hydration need caution. In practice, weigh at the same time and under the same conditions every day.<\/p>\nWhat a BMI Weight Machine Actually Measures<\/h2>\n
Where BMI Falls Short<\/h2>\n
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What a Body Composition Scale Adds<\/h2>\n
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Three Tiers Side by Side<\/h2>\n