Method
Prepare a boiling-water canner. Heat jars in simmering water until ready for use; do not boil. Wash lids in warm soapy water and set bands aside.
Combine crushed strawberries and bottled lemon juice in a 6- or 8-quart saucepan. Gradually stir in pectin.
Bring to a full rolling boil over high heat, stirring constantly. Add all the sugar, stirring to dissolve. Return to a full rolling boil and boil hard for 1 minute, stirring constantly. Remove from heat and skim foam if needed.
Ladle hot jam into hot jars, leaving 1/4-inch headspace. Remove air bubbles, wipe rims, center lids, and tighten bands fingertip-tight.
Process jars in a boiling-water canner for 10 minutes, adjusting for altitude. Turn off heat, remove the lid, and let jars stand 5 minutes.
Remove jars and cool undisturbed for 12 to 24 hours. Check seals; refrigerate any unsealed jars.