Setting up a roblox magnitude distance check script is one of those foundational skills you'll find yourself using in almost every single project you start. Whether you're trying to figure out if a player is close enough to open a door, making an NPC chase a target, or even building a custom shop system that only opens when you're standing near the counter, magnitude is the tool you're going to reach for.
It sounds like a fancy math term, and technically it is, but in the context of Roblox Luau, it's remarkably simple. You don't need to be a geometry whiz to get this working because the engine does the heavy lifting for you. Let's break down how to write one and, more importantly, how to use it without making your game laggy.
Why magnitude is your best friend
In the old days of game dev, if you wanted to find the distance between two points, you'd have to manually use the Pythagorean theorem. You'd subtract the X, Y, and Z coordinates, square them, add them together, and then find the square root. It was a headache to type out every time.
Roblox makes this way easier. Every Vector3 value has a property called .Magnitude. If you subtract one position from another, you get a new vector that represents the gap between them. By checking the magnitude of that "gap" vector, you get the exact distance in studs.
It's honestly one of the most reliable ways to handle interactions. Some people try to use Touch events for everything, but those can be incredibly finicky. Sometimes they don't fire if the player is standing still, or they fire twenty times in a second because of a physics glitch. A distance check is much more "stable"—it tells you exactly where things are, regardless of whether they're moving or touching.
Writing your first basic check script
Let's look at the simplest version of a roblox magnitude distance check script. Imagine you have two parts in your workspace named "PartA" and "PartB". You want to know how far apart they are.
```lua local partA = workspace.PartA local partB = workspace.PartB
local distance = (partA.Position - partB.Position).Magnitude
print("The distance between the parts is: " .. distance) ```
That's literally it. The parentheses around partA.Position - partB.Position are important because you want to subtract the positions first to get the vector, and then get the magnitude of that result. If you did partA.Position - partB.Position.Magnitude, the script would get confused and probably throw an error because you'd be trying to subtract a single number from a 3D coordinate.
Applying this to players and NPCs
Usually, you aren't just checking the distance between two static bricks. You probably want to see if a player is near an object. This is where things get a bit more interesting because players are models, not parts.
When you're checking a player's position, you almost always want to reference their HumanoidRootPart. It's the invisible box in the center of every character that acts as the primary coordinate for where that player is in the world.
Here's a practical example of a script that checks if the player is close to a "Secret Button":
```lua local button = workspace.SecretButton local maxDistance = 10 -- How close the player needs to be
game:GetService("RunService").Heartbeat:Connect(function() local player = game.Players.LocalPlayer if player and player.Character and player.Character:FindFirstChild("HumanoidRootPart") then local hrp = player.Character.HumanoidRootPart local distance = (hrp.Position - button.Position).Magnitude
if distance < maxDistance then print("You're close enough to press the button!") end end end) ```
In this case, I used RunService.Heartbeat. This runs every single frame. For a local script handling UI prompts, this is usually fine, but you have to be careful about how many of these you have running at once.
Making it efficient with MagnitudeSquared
Here is a little secret that pro scripters use: calculating magnitude is actually a bit "expensive" for the computer. To get the magnitude, the CPU has to do a square root calculation. While one or two checks won't hurt, if you have 100 NPCs all checking the distance to 50 different players every frame, that math starts to add up and can tank your frame rate.
If you don't need the exact number of studs and just want to know if someone is "close enough," you can use .MagnitudeSquared (or just multiply your target distance by itself).
Basically, instead of checking if distance < 10, you check if (pos1 - pos2).MagnitudeSquared < 100. Since you aren't forcing the computer to find the square root, it's much faster. It's a small optimization, but it's a good habit to get into if you're building a large-scale game.
Real-world examples for your game
Let's look at a couple of ways you might actually use a roblox magnitude distance check script in a real project.
1. The custom proximity prompt
Roblox has a built-in ProximityPrompt object, and it's great. But sometimes, you want something that looks or feels different—maybe a UI that fades in smoothly as you walk toward a chest.
You can set up a script that calculates the distance and maps it to the TextTransparency or ImageTransparency of a BillboardGui. As the magnitude gets smaller, the transparency gets lower, making the icon "glow" as you approach.
2. Simple Enemy AI
If you're making a zombie game, you don't always need complex pathfinding. Sometimes you just need the zombie to look at the player and walk forward if they get too close.
A server-side script can loop through all the players in the game, check their magnitude relative to the zombie, and find the closest one. If that distance is under 50 studs, the zombie starts chasing. If the distance exceeds 60 studs, the zombie gives up and goes back to wandering.
Common pitfalls to watch out for
Even though magnitude is easy, there are a few things that trip people up.
First, don't forget the Y-axis. Magnitude checks distance in 3D space. If you have a button on the ground and a player is standing 20 feet directly above it on a bridge, the magnitude might still be quite large even though they are "on top" of it. If you only want to check distance on a flat plane (ignoring height), you should create a new Vector3 that zeroes out the Y-axis before checking the magnitude.
lua local pos1 = partA.Position local pos2 = partB.Position local flatDistance = (Vector3.new(pos1.X, 0, pos1.Z) - Vector3.new(pos2.X, 0, pos2.Z)).Magnitude
Second, mind the server-client boundary. If you run a distance check on a LocalScript, it's fast and responsive, but it's not "secure." A hacker could easily spoof their position to make the script think they are standing right next to a gold pile. Always double-check important distances on the server before giving players rewards or processing combat hits.
Lastly, don't over-loop. You rarely need to check a distance every single frame (60 times a second). For things like a shop menu or an NPC, checking 5 or 10 times a second is usually plenty and saves a ton of processing power. You can use a simple task.wait(0.1) inside a while true do loop instead of connecting to RenderStepped.
Wrapping it up
The roblox magnitude distance check script is a tool you'll use for the rest of your dev career. It's more reliable than touched events and way more flexible than simple zones. Once you get the hang of subtracting positions and grabbing that magnitude property, you can start building much more interactive and dynamic worlds.
Just remember to keep an eye on performance if you're doing hundreds of checks, and always consider whether you need a 3D distance or a flat 2D one. Once you've got those basics down, you're pretty much set to handle any proximity-based logic your game needs. Happy scripting!