Solvit Vehicle Pet Safety Harness (Click an image to close window and continue shopping) Harness Size Chest Neck Pet Size (weight) Small 12 to 21 12 to 18 6 to 25 lbs Medium 15 to 24 16 to 24 20 to 55 lbs Large 18 to 33 18 to 28 45 to 85 lbs Extra-Large 23 to 40 24 to 32 60 to 120 lbs Small Dog with Harness Medium Dog with Harness To size, measure around your pet's chest ("A") and neck ("B") in inches.   Refer to sizing chart shown above. Large Dog with Harness X-Large Dog with Harness