Combine sugar, water and the lemon juice in a Dutch oven or a heavy-bottomed saucepan. Stir and bring to the boil.
For the jam, choose a larger pan. For example, I use a 4 liter pan for these amounts. Besides, I don't recommend making more than 2 kg of strawberries at once.
In a 7-10 liter pot you can make 5 kg.
When you boil a lot of fruit at once in a single pan, there is a great chance to turn it into porridge. Also, the fruit won't be properly candied.