Pen Needle Length Guide: 4 mm vs 5 mm vs 6 mm vs 8 mm

Pen needles come in lengths from 4 mm to 12.7 mm and gauges from 29G to 32G. For most adults, shorter needles are now the common choice. This guide explains the sizes, what the numbers mean and what to ask your healthcare provider.

Pen needle sizes at a glance

Why shorter needles are the common choice

Insulin is meant to go into the fat layer under the skin, not into muscle. Research on skin thickness shows that the skin itself is only about 2 to 2.5 mm thick in most adults, whatever their body size. That is why a 4 mm needle is long enough to pass through the skin and reach the fat layer for most people.

Longer needles raise the chance of injecting into muscle by mistake. Insulin injected into muscle can be absorbed faster and less predictably, which can affect blood sugar. International injection technique recommendations therefore favor 4 mm pen needles for most adults and children.

What the gauge number means

The gauge (G) is the thickness of the needle. A higher number means a thinner needle: 32G is thinner than 31G, which is thinner than 29G. Many people find thinner needles more comfortable. Very thin needles can make injection of larger doses take a little longer, so hold the pen in place for the time stated in your pen's instructions.

Injection tips

• With a 4 mm needle, most adults can inject straight in at 90 degrees without pinching the skin.
• Children and very lean adults may be advised to pinch up the skin or inject at an angle; follow your provider's advice.
• Rotate injection sites to avoid lumps under the skin (lipohypertrophy).
• Hold the pen in place for the count your pen's instructions give after pressing the button.

Use a new needle every time

Pen needles are sterile and single-use. A used needle gets duller and can bend or bur, which can make injections more painful and may contribute to skin problems. Remove the needle from the pen after each injection and put it in a sharps container.

Will EasyTouch pen needles fit my pen?

The manufacturer states that EasyTouch pen needles fit most commonly used insulin pens that take screw-on pen needles. Check your pen's instructions to confirm.

Shop pen needles

Browse all EasyTouch pen needles in 4, 5, 6, 8 and 12.7 mm, including the 32G 4 mm pen needles and safety pen needles. Each box contains 100 needles, and standard shipping is free on orders of $49 or more.

This article is general information, not medical advice. Ask your healthcare provider which needle length and gauge are right for you.