Add chopped watermelon to a blender and purée until smooth.

Line a fine mesh sieve with folded cheesecloth or a jelly strainer bag. Pour the puréed watermelon through the sieve into a large bowl or measuring cup.

Measure out 4 cups of watermelon juice. Reserve leftover juice for later.

Transfer watermelon juice to a saucepan, add lime juice and pectin, and bring to a boil without sugar.

Boil for 1 minute and then whisk in sugar until dissolved. Boil for another minute.

Ladle the mixture into prepared jars, leaving 1/4-inch headspace.

Wipe rims with a clean towel and apply lids until fingertip tight.

Refrigerate for up to 3 weeks or can by processing in a hot water canner for 10 minutes.