Certo is the pectin brand I use and they have a great recipe leaflet inside their boxes here is the jams that i typically make!

INGREDIENTS

• Certo Light Pectin 1 Box
• Fruit (strawberries) 4 1/2 Cups
• Sugar 7 Cups
• Canning Jars, Sealers, and Lids

PROCESS

• Mix Fruit and Pectin Crystals in Pot and bring to boil on High Heat.
• Add Sugar
• Boil again for 1 min
• Stir and Skim with no heat for 5 min
• Pour directly into Jars and seal immediatly
• set on counter with cloth over top until all the lids have popped (DO NOT PUSH THE LIDS IN THEY MAY NOT SEAL PROPERLY)
• Leave for at least 24 Hours at Room Temp so the Jam has time to set.

If I am making a strawberry rhubarb jam I subtract one cup of the strawberries and replace with one cup of rhubarb instead.

Generally I am making much more than one batch of this recipe in which case I double or triple the recipe at times and have had no problems yet!