Values and units

PurgeTSS writes plain numeric values into your TSS files. Titanium decides how to interpret them.

The short version

Numeric values produced by PurgeTSS utility classes are unitless. When PurgeTSS compiles rounded-lg to:

'.rounded-lg': { borderRadius: 8 }

the 8 is not a pixel value. Titanium reads it at runtime using the unit declared in tiapp.xml:

<ti:app>
  <property name="ti.ui.defaultunit" type="string">dp</property>
</ti:app>

The Alloy project template has used dp by default for years, so most PurgeTSS projects are working with density-independent pixels, not raw pixels. In practice, borderRadius: 8 usually means 8dp, not 8px.

Why this matters

Saying rounded-lg gives you "8 pixels" is only correct if your tiapp.xml explicitly sets ti.ui.defaultunit to px. Most projects do not.

A more accurate way to describe it is:

rounded-lg applies borderRadius: 8 — which Titanium interprets as 8 units of ti.ui.defaultunit, defaulting to dp on standard Alloy projects.

This applies to every utility class that sets a dimension:

• Spacing: m-*, p-*, mt-*, mb-*, mx-*, my-*, top-*, left-*, right-*, bottom-*
• Sizes: w-*, h-*, size-*, wh-*
• Corners: rounded-*, border-radius-*
• Borders: border-* (width)
• Typography: text-* (font size), letter-spacing-*, line-spacing-*
• Shadows: drop-shadow-*, shadow-radius-*
• Elevation: elevation-*, max-elevation-*
• Transforms: translate-*, move-by-*
• Offsets: x-offset-*, y-offset-*

Valid values for ti.ui.defaultunit

Titanium recognizes these unit identifiers:

Value	Meaning	Notes
dp	Density-independent pixels	Alloy template default. Good default for cross-density consistency.
dip	Alias for dp	Same as dp.
px	Raw pixels	Usually a poor fit for UI sizing on high-DPI devices.
mm	Millimeters	Physical measurement.
cm	Centimeters	Physical measurement.
in	Inches	Physical measurement.
pt	Points (1/72 inch)	Physical measurement.
system	Platform default	iOS uses points; Android uses pixels. This is inconsistent across platforms.

Forcing pixels explicitly

Some PurgeTSS classes use explicit pixel values written as strings:

'.border-radius-px': { borderRadius: '1px' }
'.w-px':             { width: '1px' }
'.h-px':             { height: '1px' }

If a value includes its own suffix, such as '1px', '2pt', or '4mm', Titanium uses that unit directly and ignores ti.ui.defaultunit.

Use these when you actually need a 1px line or another exact unit.

Percentages are unit-independent

Fractional utility classes produce percentage strings. Titanium resolves those against the parent size, not against ti.ui.defaultunit:

'.w-1/2':  { width: '50%' }
'.h-full': { height: '100%' }

These behave the same no matter which default unit your app uses.

Titanium constants are unit-independent

Utility classes that resolve to Titanium layout constants also ignore units:

'.w-auto':   { width: Ti.UI.SIZE }
'.h-screen': { height: Ti.UI.FILL }

Ti.UI.SIZE and Ti.UI.FILL are layout directives, not numeric dimensions.

Checking your project's setting

Open tiapp.xml and look for:

<property name="ti.ui.defaultunit" type="string">dp</property>

If that property is missing, Titanium falls back to system. That means iOS and Android can interpret the same number differently, so it is better to set dp explicitly.

Summary

• PurgeTSS writes unitless numeric values into app.tss.
• Titanium resolves those values using ti.ui.defaultunit in tiapp.xml.
• In most Alloy projects, that unit is dp, not raw pixels.
• Values ending in -px (written as quoted strings) force raw pixels regardless of the project setting.
• Percentage-based and auto/screen utilities are unit-independent.