How long of a needle should I use for injecting?
Abbreviations
BMI - body mass index, calculator 1 or calculator 2, explanation that BMI doesn't reflect health, alternate discussion of same
IM - intramuscular
SC - subcutaneous
Overview of IM injection sites
Hip or dorsogluteal area (gluteus maximus and minimus)
Ventrogluteal area (gluteus medius)
Thighs (rectus femoris,
vastus lateralis)
Arms (deltoid,
triceps, but I'm not including triceps as I can't find good data and I don't think that many people use it)
Overview of SC injections
Recent reports indicate that SC administration of testosterone esters is an acceptable alternative to IM injections. [Source 1, Source 2]
Needle sizes
7mm - 1/4in or .25in
8mm - 5/16in
10mm - 3/8in or .375in
11mm - 7/16in
13mm - 1/2in or .5in
16mm - 5/8in or .625in
22mm - 7/8in or .875in
25mm - 1.0in
30mm - 1.25in
40mm - 1.5in
The first 5mm is always SC no matter what. So it is necessary that the needle penetrate at least 5mm beyond the SC tissue into the muscle. Anything less than this, including "shallow IM," is inecting SC. (The drug release rate from shallow IM is indistinguishable from SC.)
Minimum needle length needed for Intramuscular (tissue depth is the mean followed by Standard Deviation)
BMI 18.5-24.9 (termed normal)
Male
Dorsogluteal - 1.5in needle
Ventrogluteal - 1.25in needle
Rectus Femoris - 5/8in needle
Vastus Lateralis - 1/2in to 5/8in needle
Deltoid - "insert the needle to a depth of 1.5 cm for 18.5 ≦ BMI < 30.0 and 2.0 cm for BMI ≧ 30.0." 15mm is 5/8ths inches.
Female
Dorsogluteal - data not available
Ventrogluteal - 1.5in needle
Rectus Femoris - data not available
Vastus Lateralis - data not available
Deltoid - Minimum unknown, "1in needle is good for all patients up to BMI 35"
BMI 25–29.9 (termed overweight)
Male
Dorsogluteal - 1.5in needle (thickness 43.71 ± 3.76mm)
Ventrogluteal - 1.25in needle (thickness 31.2mm)
Rectus Femoris - 1.0in needle (thickness, 20.77 ± 5.00mm)
Vastus Lateralis - 5/8in needle (thickness, 15.53 ± 2.49mm)
Female
Dorsogluteal - 2.0in needle (thickness 68.79 ± 14.99mm)
Ventrogluteal - 2.0in needle (thickness 50.5mm)
Rectus Femoris - 1.0in needle (thickness, 23.94 ± 6.53mm)
Vastus Lateralis - 1.0in needle (thickness, 22.04 ± 7.31mm)
Male
Dorsogluteal - 2.0in needle (thickness, 48.48 ± 8.86mm)
Ventrogluteal - 1.5in needle (thickness 37.0mm)
Rectus Femoris - 1.0in needle (thickness, 22.84 ± 6.77mm)
Vastus Lateralis - 1.0in needle (thickness, 17.78 ± 5.59mm)
Female
Dorsogluteal - 2.0in needle (thickness, 67.77 ± 12.97mm
Ventrogluteal - 2.0in needle (thickness 54.3mm)
Rectus Femoris - 1.25in needle (thickness, 29.94 ± 6.91mm)
Vastus Lateralis - 1.25in needle (thickness, 27.14 ± 7.59mm)
BMI ≥35
Male
Dorsogluteal - N/A (thickness, 76.50mm)
Ventrogluteal - 2.0in needle (thickness 41.3mm)
Rectus Femoris - 1.25in needle (thickness, 32.00mm)
Vastus Lateralis - 1.0in needle (thickness, 25.40mm)
Female
Dorsogluteal - N/A (thickness, 69.30 ± 13.92mm)
Ventrogluteal - N/A (thickness 59.2mm)
Rectus Femoris - 1.5in needle (thickness, 38.66 ± 7.93mm)
Vastus Lateralis - 1.25in needle (thickness, 32.37 ± 8.19mm)
Q. Why didn't you put this in a table?
A. So it would display correctly on any device. I'm about the info, I'm not a Web designer.
Sources
Examination of Subcutaneous Tissue Thickness in the Thigh Site for Intramuscular Injection in Obese Individuals by Zaybak, İsmailoğlu, İsmailoğlu in the Journal of Ultrasound in Medicine published 12 August 2015.
Does obesity prevent the needle from reaching muscle in intramuscular injections? by Zaybak, Güneş, Tamsel, Khorshid, Eşer in JAN Original Research published 29 January 2007.
Appropriate Needle Insertion Depth for Intramuscular Injection Based on Assessment of BMI by Takahashi, Kikuchi, Miura, Ishida in J-Stage published 2014, used Google Translate
Influence of gender, BMI and body shape on theoretical injection outcome at the ventrogluteal and dorsogluteal sites by Larkin, Ashcroft, Hickey, Elgellaie in Journal of Clinical Nursing Volume27, Issue1-2 published January 2018
Definition of needle length required for intramuscular deltoid injection in elderly adults: an ultrasonographic study by Cook, Williamson, Pond, Journal of Vaccines in 2005
Links to unit converters