How to change the radius on a collider in Unity
To change a collider's radius in Unity, select the GameObject with the collider attached, then in the Inspector panel find the collider component and modify the Radius field directly. The change takes effect immediately in both the Scene view and Play mode. Different collider types — Sphere, Capsule, Circle — each have a radius property you can adjust the same way, though some colliders like Box use different dimensions.
The radius value is measured in Unity units. A radius of 1 means the collider extends 1 unit from its center point in all directions (for sphere colliders) or along its defined axis (for capsule colliders). You can type a number directly into the field, use the up and down arrows to increment by 0.1, or click and drag the field value to change it smoothly.
Key Takeaways
- Select the GameObject, locate the collider component in the Inspector, and change the Radius value in the same panel where you see other collider settings.
- Sphere colliders, Capsule colliders, and Circle colliders all have a Radius property; Box colliders use Size instead.
- Changes to radius take effect immediately without requiring Play mode, so you can see the collider boundary adjust in real time in the Scene view.
- Radius is measured in Unity units, and the value represents the distance from the collider's center to its edge.
Accessing the collider component in the Inspector
Open the scene containing the GameObject you want to modify. Click on the GameObject in the Hierarchy panel or directly in the Scene view. The Inspector panel on the right side of the screen will display all components attached to that object, including any colliders.
Scroll down in the Inspector if necessary to find the collider component. You will see a header with the collider type — for example, "Sphere Collider" or "Capsule Collider" — followed by a list of properties. The Radius field appears near the top of the collider's properties, usually just below the "Is Trigger" checkbox.
Modifying the radius value
Click directly on the number in the Radius field to select it. You can then type a new value and press Enter to confirm. Alternatively, position your cursor over the field label "Radius" itself and click and drag left or right to decrease or increase the value smoothly — dragging right increases the radius, dragging left decreases it.
If you prefer to increment by small amounts, click the up or down arrow buttons that appear to the right of the Radius field. Each click changes the value by 0.1 units. For large changes, typing the number directly is fastest.
Seeing the radius change in real time
As soon as you modify the Radius value, the collider's visual boundary updates in the Scene view. You will see a wireframe outline showing the new collider size. This happens whether the game is running or paused, so you can adjust the radius and immediately see how it affects the collider's coverage without entering Play mode.
If the collider outline is not visible in the Scene view, make sure the GameObject is selected and that gizmos are enabled. In the top right of the Scene view, click the "Gizmos" dropdown and ensure collider visualization is turned on.
Radius differences between collider types
A Sphere Collider's radius extends equally in all directions from the center point, creating a perfect sphere. A Capsule Collider's radius defines the thickness of the capsule shape, while its Height property controls how tall the capsule is. A Circle Collider (used in 2D) works similarly to a Sphere Collider but in two dimensions only.
Box Colliders do not use a radius property at all — instead they use a Size property with X, Y, and Z dimensions. If you need to adjust a Box Collider's dimensions, modify the Size field rather than looking for a Radius field. Cylinder and other primitive colliders also use different property names depending on their shape.
Adjusting radius through code
If you want to change a collider's radius during gameplay or through a script, you can access it programmatically. For a Sphere Collider, use GetComponent<SphereCollider>().radius = newValue; where newValue is the new radius. For a Capsule Collider, use GetComponent<CapsuleCollider>().radius = newValue; in the same way.
Changes made through code take effect immediately, just like changes in the Inspector. This is useful for mechanics where the collider size needs to change based on game state — for example, a character growing larger or a projectile expanding on impact. Always ensure the GameObject has the collider component attached before trying to access it, or the GetComponent call will return null and cause an error.
Common issues when changing radius
If the collider does not appear to change size visually, check that you are modifying the correct collider component. GameObjects can have multiple colliders attached, and only the one you are editing will change. Also verify that the collider is not set to "Is Trigger" if you expect it to interact with physics — trigger colliders do not participate in physics calculations, only collision detection.
If the radius change does not affect gameplay behavior, make sure the Rigidbody component (if present) has not been set to Kinematic mode, which prevents physics interactions. Additionally, check that the collider's layer is not being ignored by the physics settings or by other colliders' layer masks.
Frequently Asked Questions
Can I change the radius of a collider while the game is running?
Yes. You can modify the radius through code using GetComponent, and the change takes effect immediately. You can also pause the game, select the GameObject in the Hierarchy, and edit the radius in the Inspector while paused, then resume play.
What happens to physics when I change the radius?
Physics recalculates based on the new collider size on the next physics frame. If the collider now overlaps with other objects, Unity will generate collision or trigger events depending on the collider settings. Existing velocity and forces are not affected by the radius change itself.
Does changing radius affect performance?
Changing the radius value itself has no performance cost. However, making a collider much larger increases the number of objects it might collide with, which can increase physics calculations. Making it smaller generally improves performance by reducing collision checks.
Can I animate the radius changing over time?
Yes, using either an Animation Curve in the Animator or a coroutine that gradually changes the radius value each frame. For example, a coroutine can loop and increment the radius by a small amount per frame until it reaches the target value, creating a smooth size transition.
Why does my collider radius not match the visual mesh?
Colliders are independent of the visual mesh and do not automatically scale with it. If you scale the GameObject using the Transform Scale property, the collider scales with it, but if you change only the mesh or model, the collider stays the same. Adjust the radius manually to match your visual needs.