All together and altogether are homophones, which means they sound alike, but they have different meanings. I, for one, find it easy to confuse them, so the explanation below is for my benefit as well as anyone else who might be interested.

Five ducklings all together

All together, a two-word phrase, means collectively, with each other, everyone doing something all at once or all in one place:

• We gathered round the piano and sang the folk song all together.

      (It’s possible to break up this two-word saying as in “We all gathered round the piano and sang the folk song together.)

• The old man decided to throw a party because he wanted to see his grandchildren all together before his illness became too severe.
• She asked me to collect up the dirty clothes left scattered about the house and put them all together in a pile near the washing machine.

Altogether lovely snowdrop

Altogether, spelled as one word, means entirely, completely or in total:

• They were altogether too tired to continue on foot and opted to take the bus.
• The Criminal Courts Charge was introduced to such universal condemnation that six months later it was abolished altogether.
• The book cost £10.50 and the magazine cost £5.25, so that was £15.75 altogether.

You could use both expressions in one sentence like this:

• The family were forced to live all together in one room, but they dared not complain that the room was altogether too cramped for fear of being evicted.