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Bluetooth-enabled hydrometers have fundamentally changed how I manage fermentation. Before I owned one, my gravity readings were snapshots, a data point every 2–3 days, with guesswork between them. The Tilt floating in the fermenter gives me a continuous curve: I can see exactly when fermentation started, how fast gravity dropped, when it slowed, and when it plateaued at FG. That data has made me a better brewer not by replacing any skill, but by showing me what was actually happening in the fermenter versus what I assumed was happening. Here’s a practical guide to the Bluetooth hydrometer category in 2025.
How Bluetooth hydrometers work
Bluetooth hydrometers are elongated sealed floats containing a microcontroller, accelerometer, temperature sensor, and Bluetooth radio. They measure specific gravity by measuring their tilt angle in the liquid, denser liquid holds the float more upright; less dense liquid allows it to tilt more. The angle is read by the accelerometer and converted to specific gravity via a calibration curve. Temperature is measured by an onboard sensor. Both readings are transmitted via Bluetooth every 30–120 seconds to a phone or Raspberry Pi relay. The floats are sealed and sanitized externally before placement, internal components never contact the beer.
Tilt Hydrometer
The Tilt ($130–150) is the original and most widely adopted Bluetooth hydrometer. Available in 8 colors, each with a different default calibration range. Connects to the Tilt app on iOS or Android; also connects to a Raspberry Pi running TiltPi for continuous cloud logging to Google Sheets. Calibration: tilt calibration is adjustable in the app by comparing Tilt readings against manual hydrometer readings on the same sample. Accuracy after calibration: ±0.002 SG, ±1°F. The eight-color system allows using different colors for different fermenters simultaneously, each color appears as a separate device in the app. Brewfather Premium and Brewer’s Friend both support Tilt integration for displaying readings within the batch record.
Rapt Pill
The Rapt Pill ($75–95) uses wifi rather than Bluetooth, which eliminates the range limitation of Bluetooth devices and removes the need for a Raspberry Pi relay. It connects directly to your home wifi network and uploads readings to the Rapt cloud platform. The Brewfather Premium integration is built-in, enable it in Brewfather’s device settings and Rapt Pill readings appear in the active batch record automatically. Form factor: pill-shaped, slightly smaller than the Tilt. Calibration and accuracy are comparable to the Tilt. The wifi connectivity and lower price make the Rapt Pill the better first choice for most new buyers in 2025.
iSpindel (DIY option)
The iSpindel is an open-source DIY Bluetooth hydrometer using a Wemos D1 Mini ESP8266, MPU-6050 accelerometer/gyro, DS18B20 temperature sensor, and a LiPo battery in a custom 3D-printed enclosure. Total parts cost: $15–25. Performance is comparable to commercial units after calibration. The DIY process requires soldering, 3D printing or sourcing a printed enclosure, and flashing custom firmware (well-documented on the iSpindel GitHub). For technically inclined homebrewers who want the functionality at minimum cost, the iSpindel is a proven and well-supported project with an active community.
Common Questions
How do I calibrate a Bluetooth hydrometer for accurate readings?
Calibration requires at least two reference points: distilled water (1.000 SG) and a known-gravity wort or sugar solution. Prepare a sugar solution of known gravity (verified by a calibrated bench hydrometer, for example, 1.040 SG). Place the Bluetooth hydrometer in the sugar solution, record the raw reading, then record the bench hydrometer reading. Repeat in distilled water. In the device app (Tilt app, Rapt dashboard, or iSpindel web interface), enter the correction offset or calibration coefficients based on these two reference points. The calibration curve is linear for most devices, two points define it completely. Recalibrate after any firmware update and when readings drift more than 0.003 SG from bench hydrometer readings. Temperature affects accuracy, calibrate at the temperature range typical for your fermentation (most devices compensate automatically, but calibrating at a representative temperature improves accuracy).
