What is unit of measurement in flutter

Question

as usual, we use dp for Android and pt(point) for ios as a unit of measurement.

1 pt = 1/72 inch

1 dp = 1/160 inch

But i don't what is unit of measurement in flutter

example:

SizedBox(height: 16.0)

or

TextStyle(fontSize: 23.0)

It just a double number, how many dp or pt equal to 1.0 (flutter)? How is it calculated?

Answer 1

From https://docs.flutter.io/flutter/dart-ui/Window/devicePixelRatio.html :

The number of device pixels for each logical pixel. This number might not be a power of two. Indeed, it might not even be an integer. For example, the Nexus 6 has a device pixel ratio of 3.5.

Device pixels are also referred to as physical pixels. Logical pixels are also referred to as device-independent or resolution-independent pixels.

By definition, there are roughly 38 logical pixels per centimeter, or about 96 logical pixels per inch, of the physical display. The value returned by devicePixelRatio is ultimately obtained either from the hardware itself, the device drivers, or a hard-coded value stored in the operating system or firmware, and may be inaccurate, sometimes by a significant margin.

The Flutter framework operates in logical pixels, so it is rarely necessary to directly deal with this property.

Answer 2

The unit of measure in Flutter is Logical Pixels. Logical Pixels are equivalent to cm or inches and do not vary depending on the resolution the same way a ruler doesn't.

1 cm = 38 logical pixels

1 in = 96 logical pixels

Logical pixels are different from device (also called physical) pixels. Device/physical pixels are the number of dots/points in the display that emit light.

This numbers were chosen for historic reasons and come from 1980. Source: Microsoft