how to limit seekbar

In SeekBar you can set only max value.

<SeekBar android:id="@+id/SeekBar01"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:max="50"/>

And,
You cannot directly set the minimum value to the seekbar.

 SeekBar mSeekbar = (SeekBar) findViewById(R.id.SeekBar01);

    mSeekbar.setOnSeekBarChangeListener(new OnSeekBarChangeListener()
    {
       public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser)
       {
            length_edit.setText(Integer.toString(progress + 20));
       }

      public void onStartTrackingTouch(SeekBar seekBar) {}

      public void onStopTrackingTouch(SeekBar seekBar) {}
    });

As you see min progress you can sum with min which I would like – in your case 20.