OneScale — touchscreen pocket scale

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grams

Place the carrier on the screen

raw pressure: 0.000 · contacts: 0

Rest a conductive carrier (e.g. a slightly damp metal spoon) anywhere on this area, then put the object on it.

Before you start

Find a carrier: something conductive that the screen registers as a touch even without your finger. A metal teaspoon with a slightly damp bowl works well. A folded piece of anti-static bag or a coin on a damp paper corner also works.
Find a reference weight you know precisely: a 1 g calibration weight, a US nickel (5.000 g), a 1 euro-cent coin (2.30 g), or a new A4 sheet of 80 g/m² paper folded up (≈ 5.0 g).
Put the phone flat on a table and keep everything still during capture.

Tip: heavier references (2–10 g) calibrate more accurately than 1 g, because the signal is further above the sensor noise.

Step 1 · Zero

Place the empty carrier on the capture area below and don't touch anything.

0.000 raw

Step 2 · Reference weight

Keep the carrier in place and put your reference weight on it.

Reference mass (grams)

0.000 raw

Calibration saved

The calibration is stored on this device. Re-calibrate whenever you switch carriers or the readings drift.

Press the area below with your finger, varying how hard you press for a few seconds.

0.000

raw pressure

Waiting for touches…

What this app does

OneScale reads the touch pressure value your phone reports for each contact on the screen and converts it to grams using a linear calibration you set with a known reference weight.

Why you need a "carrier"

Capacitive screens only register conductive objects (like fingers). A plastic bead or a pill sitting directly on the glass is invisible to the screen. So you place a conductive carrier — a slightly damp spoon is the classic choice — on the screen, tare it away, and then weigh objects by putting them on the carrier.

Which phones can actually do this

iPhone 6s → XS (3D Touch): these have a real force sensor under the glass and give the best results (roughly 0–400 g range).
Most Android phones: report a pseudo-pressure derived from the contact area. With a soft/damp carrier this still changes with load, so calibration can work — but accuracy is rough.
iPhone 11 and newer: Apple removed the force sensor. The screen reports no usable pressure, and no app (web or native) can weigh things on it. Use the Sensor check to test your device.

Accuracy expectations

Even on 3D Touch hardware this is a party trick, not a lab scale: expect roughly ±5–15% after a good calibration. Temperature, where the carrier sits on the screen, and how damp it is all shift the reading. Tare often and keep the reference weight comparable in size to what you weigh.

Permissions

None needed — touch pressure is part of normal browser touch events, so there's no permission prompt (unlike motion sensors or the camera). Nothing leaves your device; calibration is stored locally.