Smart Scales & Body Composition
Withings, Renpho, Garmin Index, Eufy — and OpenScale, the FOSS escape hatch.
A smart scale's actual job is trend tracking — body weight + body fat % + lean mass over weeks and months. The body-fat number any consumer scale gives you is approximate (BIA / impedance is noisy by design); the trend is what matters. Pick on app ecosystem and self-host willingness.
Sister sections: Apple Watch, Garmin, Withings & HA, Strength Logging, DEXA & Clinical Body Comp, Quantified Self DIY, BLE & Bluetooth IoT.
The defaults (paid hardware + free apps)
- ★ ★ Withings Body+ / Body Cardio / Body Scan — paid (~$100-400); the most-recommended consumer smart scale; clean Health Mate app; Apple Health + Health Connect + Garmin Connect bidirectional sync; no subscription required (Health+ is optional).
- ★ Renpho Smart Scale — paid (~$30-50); cheapest credible smart scale; Renpho app + Apple Health / Health Connect; multi-user. Lacks Wi-Fi on the cheapest models (BLE phone-side sync only).
- ★ Eufy Smart Scale — paid (~$60); similar BIA accuracy to Withings at half the price; multi-user.
- Garmin Index S2 — paid (~$150); for Garmin loyalists; Wi-Fi sync to Garmin Connect; no third-party app.
- Wyze Scale X — paid (~$50-100); Wyze app; Health Connect integration.
- Tanita BIA scales — research-grade (4-electrode segmental); ~$150-2000+; the high-end home option.
FOSS / privacy-first
- ★ ★ OpenScale — FOSS Android; reads dozens of cheap BLE smart scales (Mi Body Composition Scale, Yunmai, Beurer, certain Eufy / Renpho models, generic Xiaomi) without their cloud apps; local SQLite store; CSV export; CSV/Health Connect/Wger sync.
- The right answer if you don't want a Chinese cloud account on your scale.
- Wger integration — body weight tracker pairs with Wger workout server.
Body composition methods (accuracy reality)
| Method | Cost | Accuracy | Notes |
|---|---|---|---|
| Consumer BIA scale | $30-200 | ±3-5% body fat | Useful for trends only |
| 4-electrode BIA (Tanita / inBody) | $150-3000 | ±2-3% | Gym / clinic tier |
| DEXA scan | $50-150 / scan | ±1-2% | Gold standard for home use; see DEXA Clinics |
| Hydrostatic weighing | $50-100 / session | ±1-2% | Vintage; rare |
| Bod Pod | $40-60 / session | ±1-2% | Common in athletic centers |
| Caliper / skinfold | $20 caliper | ±3-4% w/ practitioner | Cheap, technique-dependent |
| Eyeballing / progress photos | Free | Subjective | Surprisingly useful |
★ The trend from any consistent method beats a single high-accuracy snapshot. Weigh the same way (morning, after bathroom, before food/water) for comparable numbers.
What scales actually track
- Weight (mostly accurate, ±0.1 kg on consumer scales).
- Body fat % (BIA — noisy; avoid weighing right after exercise / shower / drinking).
- Muscle mass / lean mass (derived from BF% — same noise).
- Water % (hydration — varies hugely day-to-day).
- Bone mass (mostly bunk in BIA).
- Visceral fat rating (proprietary score; trend OK, absolute number not meaningful).
Best practices
- ★ Weigh same time each day — morning, after bathroom, before eating/drinking.
- ★ Watch 7-day rolling average, not daily numbers.
- Use one scale; switching between scales is meaningless because each manufacturer's BIA model differs.
- Replace batteries annually on BLE-only scales; calibration drift is usually battery-related.
- Don't bother weighing more than once a day — water swings are larger than measurable changes.
Specialty / professional
- ★ InBody 270 / 570 / 770 — multi-frequency segmental BIA; gym / clinic tier; ~$2500-15000; what your gym's "Body Comp Day" uses.
- Tanita MC-980 — research-grade.
- BodySpec mobile DEXA — paid; truck-based DEXA scans in major US cities.
- See DEXA & Clinical Body Comp.
Home Assistant / aggregation
- ★ Withings HA integration — official; weight, BF%, lean mass, BP (if Withings BP cuff). See Home Assistant Add-ons.
- Garmin Connect HA integration — for Garmin Index S2.
- Theengs Gateway — many BLE scales advertise readings; can pull weight without an app. See BLE & Bluetooth IoT.
Cost / license honesty
- Withings Body+ — ~$100; no sub.
- Renpho / Eufy / Wyze — ~$30-100; cloud account required for the official app, but OpenScale can read them BLE-direct without one.
- Garmin Index S2 — ~$150; no sub; locked to Garmin Connect.
- OpenScale — GPL-3.0 FOSS, F-Droid + Play Store.
Pick this if…
- One-pickup answer: Withings Body+ + Apple Health / Health Connect.
- Cheapest credible: Renpho or Eufy + Health Connect / Apple Health.
- Already in Garmin ecosystem: Garmin Index S2.
- Privacy-first / no cloud account: Mi Body Comp Scale + OpenScale.
- DIY / Home Assistant nerd: any BLE scale + Theengs Gateway.
- Real accuracy required: annual DEXA + a cheap scale for trend.