Cut off the leaf and root end of the rhubarb stalks, then wash the stalks under cool water. Chop the rhubarb and place it in a large pot. Add 3 cups of water to the rhubarb in the pot.
Place the pot over medium-high heat and bring the rhubarb to a low boil. Stir regularly to prevent foaming. Reduce the heat and simmer for 15 to 20 minutes, or until the rhubarb has completely broken down and the liquid is bright pink.
Using a fine mesh strainer lined with cheesecloth, pour the rhubarb mixture into the strainer and allow the juices to drip through for 1-2 hours or more. Measure out 4 cups of juice.
Pour the 4 cups of juice into a medium saucepan. Bring to a boil over medium-high heat while stirring occasionally. Slowly add powdered pectin and stir continuously until dissolved. Bring to a full boil, then add the pre-measured sugar while stirring until dissolved. Boil for 1-2 minutes.
Ladle the jelly into prepared hot jars, leaving ¼ inch headspace. Wipe jar rims with a clean cloth. Apply 2-part canning lids and screw on the rings until finger-tight.
Process jars in a boiling water bath for 10 minutes (or 15 minutes if above 6,000 feet in elevation). Turn off the heat and let the jars sit for 5 minutes before removing.