How long until the sun is a mile in diameter?

The sun will never be a mile across, it's much larger than that - over 110 times the diameter of the Earth and a million times the Earth's volume. But the sun will not remain in its present form for ever. At the moment it is about 4.5 billion years old and is 'burning' hydrogen to produce the heat and light that we rely on for our life on earth today. So far it has burned up about 50% of its hydrogen stores meaning that it should be okay for another 5-6 billion years. But once the hydrogen is all gone the sun will begin to burn up helium in its core and at the same it will swell into a 'Red Giant', engulfing the innermost planets in our solar system as it does so. This phase will last about 500 million years before the sun shrinks back to become a very dense 'white dwarf' not much bigger than the size of the earth. Although it will be very small, the white dwarf will be extremely dense - a teaspoonful of the material it is made from will weigh more than a tonne.