Box2D pixel to meter conversion

I have a game that was written in pixels and now I want to change it to meters like(box2D do). How I need to do that. I have wached a lot of tutorials and all they have some SCALING FACTOR but when I implement it my game don’t work as I aspected. How I need to do that? For example I have a Coin and I want to make position of that coin random. I also want that coin sprite have a CircleShape (Box2D). Here are my code where I update my coin coordinates at specific time

if(time > 1.5f && !goToWallet && setUpCoin){
                coin.setCoinPosition(-100, -100); // do not show coin on the screen
                coin.update(coin.getCoinX(), coin.getCoinY());
                cam.update();
                if(showTime > MathUtils.random(5, 20) && !goToWallet){
                    coin.setCoinPosition(MathUtils.random(50, Gdx.graphics.getWidth() - 50)/100f, MathUtils.random(50, Gdx.graphics.getHeight() - 50)/100f); // random position of the screen IN PIXELS!!!
                    coin.update(coin.getCoinX(), coin.getCoinY());
                    cam.update();
                    time = showTime = 0.0f;
                }
            }

The problem is that is very easy to do in pixels, but How I need to do that in meters?

Here’s my Coin class

public class Coin {
    /*
    A lot of variables
    */

    private final float radius;
    private BodyDef body;
    private FixtureDef bodyPhysics;
    private static Box2DDebugRenderer rend;
    private static World world;
    private static CircleShape coin;

    public Coin(World world, Box2DDebugRenderer rend){
        this.rend = rend;
        this.world = world;

        body = new BodyDef();
        bodyPhysics = new FixtureDef();
        coin = new CircleShape();
        coin.setRadius(.05f);
        body.type = BodyType.StaticBody;
        bodyPhysics.shape = coin;
        world.createBody(body).createFixture(bodyPhysics);
}
public void setCoinPosition(float x, float y){
    this.x = x;
    this.y = y;
    coin.setPosition(new Vector2(x, y));
}

}