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How Do You Check If a Position Is Inside a Part in Roblox?

Convert a world position to a Roblox part’s local space and compare it with half the part’s dimensions. The method tests a rectangular box, including rotated blocks.
WorldRoblox? Length2 min Posted Quest giverVGSources Team
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For a rectangular Roblox part, convert the world-space position into the part’s local space with part.CFrame:PointToObjectSpace(position), then check whether each coordinate falls within half of the matching part dimension. This works for rotated blocks because the comparison uses the part’s own orientation.

Check a world position against a rectangular part

Use the part’s CFrame to transform the point, then compare its local X, Y, and Z values with half of the part’s size:

local function isPositionInsideBlock(part: BasePart, position: Vector3): boolean
    local localPosition = part.CFrame:PointToObjectSpace(position)
    local halfSize = part.Size * 0.5

    return math.abs(localPosition.X) <= halfSize.X
        and math.abs(localPosition.Y) <= halfSize.Y
        and math.abs(localPosition.Z) <= halfSize.Z
end

Pass the BasePart and the position you want to test. The function returns true only when the point is within the part’s local box on all three axes. Roblox’s CFrame reference describes PointToObjectSpace as converting a world-space point into object space; BasePart supplies the part’s pose through CFrame and dimensions through Size.

Choose how to treat points on a face

The example uses <=, so a point exactly on a face, edge, or corner counts as inside. Use < instead if boundary points should count as outside. This is a choice for your game logic, not a different Roblox containment API.

Why the check works for rotated blocks

A world-space point’s coordinates do not generally line up with a rotated part’s faces. PointToObjectSpace expresses the point relative to the part’s own position and orientation. In that coordinate frame, a rectangular block extends from negative half-size to positive half-size along each axis, so checking the absolute value of each coordinate tests whether the point lies within its box.

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Know what shape the test represents

This is an oriented bounding-box test. It is suitable when the intended region is the rectangular box described by the part’s CFrame and Size. Passing the three comparisons does not prove that a point is inside the occupied volume of a sphere, cylinder, wedge, union, or MeshPart.

Roblox’s WorldRoot spatial-query documentation notes that bounding-box queries can include space that a non-block shape does not occupy. For accuracy-sensitive overlap checks involving actual geometry, GetPartsInPart performs a full geometric collision check against the queried part’s occupied space. It reports overlapping parts; it is not a one-call point-containment function.

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Choose a spatial query for part-to-part overlap

If the question is whether parts overlap rather than whether one point lies inside a block, use a WorldRoot spatial query:

  • GetPartBoundsInBox or GetPartBoundsInRadius tests bounding volumes and accepts OverlapParams for filtering and related query settings. Bounding-volume queries can be more efficient but may not match the occupied geometry of irregular shapes.
  • GetPartsInPart checks occupied-volume overlap more accurately. The queried part must exist in the same WorldRoot as the parts being checked.

For new implementations, use these current overlap APIs rather than the legacy FindPartsInRegion3; Roblox’s Region3 reference directs users toward GetPartBoundsInBox with OverlapParams.

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