This is a popular subject and one that was dealt with in a flurry of posts;
Just to summarise; early embryo 40µmx25µm ~2x104µm3
L4 800µmx30µm ~6x105µm3
young adult 1000µmx60µm ~3x106µm3
Assuming the density of a worm was 1.08gcm-3 (from density gradient), then;
L4 worms weigh in at about 0.65µg per worm and young adults at about 3.2µg per worm.