Size of leashes

First thing! 

With all long lines, regular leashes or straight leashes the stress points are as follows:
1- your hand (if holding)
2- d-ring on collar/harness
3- snap or attachment to d-ring 
4- actual webbing material (sometimes this is #3, depending on width) 
5- rivets (unless at stress point) 

For combination, two piece, or two tone leashes just boost the rivets (stress point) up to #3. 

Our leash widths: 

3/4" - 20mm wide: Quite substantial, best for larger dogs or stronger dogs. Big hands. These weigh a bit- a 6ft leash is about 350gms

5/8" - 16mm wide: regular weight, most pups are pretty good with this weight. Comfortable in hand. A 6ft leash is about 250gms

1/2" - 12mm wide: lighter weight, mid to small dog. Great weight for long lines and drag lines for most pets. A 6ft leash is about 180gms. 

3/8" - 9mm wide: ultra light weight, cat-teacup-tiny pup size or those magical dogs that don't ever tug. Delicate in hand. A 6ft leash is about 120gms. 

ALL our Biothane webbing have a breaking strength of 1000lbs per inch of width (or 450kg per 25mm width)

For leashes: 

Cats, Teacup, Petite Dogs: 9mm or 12mm, stick with lighter snaps

Small to Medium Dogs: 12mm (all snaps) or 16mm (lighter snaps)

Medium to Large Dogs: 16mm (all snaps) or 20mm (all snaps)

Large to Extra Large Dogs: 20mm (all snaps) and non-pullers 16mm

For Long Lines (training, recall): 

9mm Long Line- cats, teacup, petite and small dogs

12mm Long Line- almost all dogs, larger cats 

16mm Long Line- Medium to large dogs

20mm Long Line- extra large to large dogs