DisplayMetrics metrics = new DisplayMetrics();
    WindowManager windowManager = (WindowManager) Actividad1.this.getSystemService(Context.WINDOW_SERVICE);
    if (windowManager != null) {
        windowManager.getDefaultDisplay().getMetrics(metrics);
    }
    int ancho = metrics.widthPixels;
    int alto = metrics.heightPixels;

mi_botón.setLayoutParams(new LinearLayout.LayoutParams(ancho/5, 13*ancho/100));