Is there a water calculator available where you can work out how much mash and/or sparge water you need to start with.

I have a BM 20L Plus and want to brew 20 Litres of an ESB Ale, total grain is 4.5kg, mash time is 60 minutes, boil time is 70 mins but I am not sure how much water to mash with and whether I need to sparge and if so with how much water.

Please can someone advise.