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Roblox Units
Explore the physical units used in Roblox and how they convert to metric units.

This article outlines Roblox physical units and how they convert to metric units. Understanding units is useful whenever you work with physics, as in the following examples:

Unit Conversions

In general, you can use the conversions in the following table to relate Roblox's primary units for time, length, and mass to their metric counterparts.
Unit Roblox Metric
**Time** 1 second 1 second
**Length** 1 stud 28 cm
**Mass** 1 RMU* 21.952 kg
\* RMU = Roblox Mass Unit The primary units are used to generate conversions for **derived** units such as water density and air pressure at standard conditions. The following physical properties are expressed in metric units and Roblox units, with primary unit equivalents provided in brackets. All conversions have been rounded to three significant figures.
Unit Metric Roblox
**Water Density** 1 g/cm³ 1 RMU/stud³
**Air Density** (sea level) 0.00129 g/cm³ 0.00129 RMU/stud³
**1 atmosphere** 101,325 Pa *[kg/(m s²)]* 1290 RMU/(stud s²)
**Spring Stiffness** 1 N/m *[kg/s²]* 0.0456 RMU/s²
**Spring Damping** 1 N s/m *[kg/s]* 0.0456 RMU/s
**Velocity** 1 m/s 3.57 studs/s
**Force** 1 N *[kg m/s²]* 0.163 Rowtons *[RMU stud/s²]*
**Torque** 1 N-m *[kg m²/s²]* 0.581 Rowton-studs *[RMU stud²/s²]*
The following table illustrates gravitational acceleration in Roblox units and metric units for presets in the **World** tab of [Game Settings](../studio/game-settings.md).
Preset Roblox Metric
**Classic** (default) 196.2 studs/s² 54.963 m/s²
**Realistic** (real-world) 35 studs/s² 9.8 m/s²
**Action** 75 studs/s² 21 m/s²
Roblox places limits on certain physical properties, as outlined in the following table. Details on these properties is located in the `Datatype.PhysicalProperties` documentation.
Property Minimum Maximum
**Density** (RMU/stud³) 0.01 100
**Friction** 0.0 2.0
**Friction Weight** 0.0 100
**Elasticity** 0.0 1.0
**Elasticity Weight** 0.0 100

Importance of Unit Consistency

Internally, the Roblox physics engine does not use unit conversions. You're free to define your own unit interpretations for studs (length) and RMUs (mass), but these should be used in a consistent manner throughout the experience. For example, if you decide that one stud equals one foot (30.483 cm), the unit density of water implies an RMU is equal to 62.4 lbs (28.3 kg):

1 (g/cm³) × (30.48³ cm³/ft³) = 28,317 (g/ft³) × (0.00220462 lbs/g) = 62.4 (lbs/ft³) = 1 (RMU/stud³)

Overall, it's recommended that you use standard Roblox units because it makes an experience work as expected in all scenarios, such as compatibility with VR controls.