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Question

Which syringes and needle size should I buy?

Sunny, owner notes“I wish my dog lived as long as I do.”Updated

I'm an owner, not a vet. This is not veterinary advice, so check anything medical with your own vet.

Short answer

Syringe boxes can look confusingly alike, so buy only the syringe and needle your vet or pharmacist says is right for your dog's insulin. The syringe has to match the strength of the insulin. Ask for the exact product name in writing, and for someone to show you how to use it. If you think the wrong syringe has already been used, call a vet urgently.

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Match the U number on the vial and the syringeIllustration. Top left: a vial labelled U-40, 40 units per ml, next to a red-capped syringe printed U-40, with a green tick: match. Top right: a vial labelled U-100, 100 units per ml, next to an orange-capped syringe printed U-100, with a green tick: match. Bottom: a U-40 vial next to an orange-capped U-100 syringe, with a red cross: wrong amount, don't inject, call your vet. Cap colours vary by maker, so always read the U number printed on the vial and the syringe.U-4040 unitsper mlRed capU-40MatchU-100100 unitsper mlOrange capU-100MatchNot a matchU-4040 unitsper mlOrange capU-100Wrong amount —don't inject,call your vetCap colours vary by maker.Always read the U number printedon the vial and the syringe.
Before every injection, look at two things: the U number on the vial and the U number on the syringe. Same number, go ahead. Different number, stop and ring your vet. Don't go by the cap colour alone.
Needle gauge: higher number means a thinner needleIllustration of three needles side by side, labelled 29G, 30G and 31G, drawn from thicker to thinner. Higher number means a thinner needle, and thinner needles usually feel more comfortable. Needle length is given in millimetres, for example 8 mm or 12.7 mm. Ask your vet which suits your dog.Length (mm)29G30G31GthickerthinnerHigher number = thinner needle.Thinner needles usually feel more comfortable.Length is in mm, e.g. 8 mm or 12.7 mm —ask your vet which suits your dog.
The G number runs backwards, which catches lots of people out: the bigger the number, the thinner the needle. Length is a separate number in mm, and that's one to settle with your vet.

I never give insulin amounts here. Yours comes from your vet's written plan.

What to know at home

Take the insulin box with you when you buy supplies. If the shop offers something different, get your vet or pharmacist to check it before you use it. The right markings and something you can handle comfortably matter more than what another owner likes.

Check the vial and the syringe show the same U number, every time. Insulin is labelled U-40 or U-100, and each syringe is made for one of them. Read the printed U number on the packet, not the cap colour. Our page on matching the syringe to your insulin explains why this matters so much.

Needle size: what the numbers mean

The G number on the packet is the needle's gauge, or thickness. It works backwards: the higher the number, the thinner the needle, so a 31G needle is thinner than a 29G one. The length is shown in mm, for example 8 mm or 12.7 mm.

Thinner, shorter needles usually feel more comfortable, and many dogs barely notice them. Ask your vet which gauge and length suit your dog's size and coat, and write it down for next time you shop.

  • Use a new syringe and needle every time. A used needle goes blunt and hurts more.
  • Put used needles straight into a sharps box or a strong lidded container, and ask your vet or chemist how to get rid of it safely.

What to write down

  • Insulin label and device packaging
  • Any difficulty drawing up or administering treatment
  • Which exact replacement the supplier is offering

What to ask next

Ask your vet to check the syringe and insulin go together and to watch you give an injection. If you think the wrong syringe has already been used, call a vet urgently and have the boxes with you. Don't try to fix it yourself.

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Sources

Every outside source I used is listed on the Sources page.

Related

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Which syringe matches my insulin?

The U number on the insulin and the U number on the syringe must match, every time.

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Which test strips fit my glucose meter?

Use only the strips made for your exact glucose meter.

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How do I check my diabetic dog's glucose at home?

Most owners get the hang of home testing. Let your vet pick the meter and show you how.

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What should I write in a notebook for my diabetic dog?

Food, mood, water, injection times and your questions. Keep it short.

Urgent help

Emergency or low blood sugar

Call a vet now if your dog is weak, collapsed or having a seizure.