Needle Length

Viscosity of the Medication

Thicker meds need syringes with larger bore sizes

Injection Route

Affects the size/type of syringe and needle needed (IM

Animal Size and Species

Smaller animals use smaller syringes; larger animals need larger ones

Needle Compatibility

Syringe must match correct needle gauge and length for safety

18G

For thick meds and large volume injections (e.g.

20G

General-purpose needle for large dogs

21G

Standard for medium-sized dogs and cats (IV use)

22G

For precise

23G

For delicate injections (small animals

25G

Fine needle for minimal pain (rabbits

27G–30G

Extremely fine for insulin

Thick Medication Needle Size

18G–20G

Thin Medication Needle Size

22G–25G

Large Animal IM Injection

18G–22G

Small Animal IM Injection

22G–25G

Large Animal SC Injection

20G–25G

Small Animal SC Injection

22G–25G

Large Animal IV Injection

18G–22G

Small Animal IV Injection

22G–25G

ID Injection Needle Size

25G–30G

½ inch needle (12 mm)

For SC & ID in small animals

⅝ inch needle (16 mm)

For SC injections and vaccines in small animals

1 inch needle (25 mm)

For IM in small animals and IV in cats/dogs

1½ inch needle (38 mm)

For IM in medium/large dogs

2 inch needle (50 mm)

For deep IM or IV in large animals