How do you get the distance between a player and a part?

(Player.HumanoidRootPart.Position - Part.Position).Magnitude

or this if you are using the player class instead of the model itself in game

(Player.Character.HumanoidRootPart.Position - Part.Position).Magnitude

This would get you the distance. (Change "HumanoidRootPart" to whatever part you want in the player like "UpperTorso".

You use magnitude and both of the parts positions

print((part1.Position - part2.Position).magnitude)

That code would print the distance, in studs, of the two parts

Use magnitude

local plr = game.Players.LocalPlayer

repeat wait() until plr.Character

local chr = plr.Character
local hrp = chr:FindFirstChild("HumanoidRootPart") -- Get HumanoidRootPart, but you can use Torso, UpperTorso, etc..


spawn(function()
  while wait()do

  -- check if player distance is <=10(mag) then 
  if (hrp.Position - game.Workspace["PartName"].Position).Magnitude <=10 then
    print("In mag")
    -- Your code here
        end
    end
end)

Sidenote

I see some answers already but none of them are explaining the concept of (a - b).Magnitude and are ignoring roblox has a built in function for this case.

Question

How do you get the distance between a player and a part?

Answer

Roblox has a method for player instances called :DistanceFromCharacter. You pass a Vector3 and it will return the distance from the character's head to the position you passed.

Example Code

In this code it will get the distance from part to the player's head then will output the distance.

local player = ... --// reference to your player
local part = --// reference to your part

local distance = player:DistanceFromCharacter(part.Position)

print(player.Name, "is", distance, "studs away!")

Extra Resources

Information

(broad explanation incoming...)

where a and b are both vectors, a - b will be the difference between those vectors. the .Magnitude property will return the length of a vector, invoking it on the difference of a - b will result in the distance between a and b.

Links:

(For a rigerous concept on how (a - b).Magnitude works: ) https://en.wikipedia.org/wiki/Euclidean_distance

(Side Route API Documentation for DistanceFromCharacter since the main page is down) https://developer.roblox.com/en-us/api-reference/class/Player