Quick answer
31G is thinner than 30G. The gauge number runs backwards: higher means thinner. On a fixed-needle insulin syringe the 31G needle is about 0.26 mm across and the 30G about 0.31 mm, a difference most people feel as "slightly less" rather than "painless". The bigger choice is usually the barrel that comes attached: 31G needles come on 0.3 and 0.5 mL syringes, 30G on the 1 mL.
Side by side
Rows that differ are highlighted. Values come from the product records for the two products named in the header.
31G Insulin Syringes 31G, 0.5 mL (100-count) |
30G Insulin Syringes 30G, 1 mL (100-count) |
|
|---|---|---|
| GaugeNeedle thickness. A higher number is a thinner needle: 31G is thinner than 30G. Glossary | 31G | 30G |
| CapacityHow much liquid the barrel holds. Smaller barrels have more space between the lines, so small amounts are easier to read. Glossary | 0.5 mL | 1 mL |
| MarkingsU-100 means 100 units to the millilitre, so one unit is 0.01 mL. A mL scale is marked in tenths. Glossary | U-100 | U-100 |
| Smallest lineWhat one line on the barrel is worth. Half-unit lines let you read 0.005 mL; a 1 mL syringe is usually marked in 2-unit steps. Glossary | 1 unit | 2 units |
| Needle lengthLength of the needle. 4–8 mm is the usual range for under-the-skin use; longer is for muscle. Glossary | 8 mm | 8 mm |
| Needle connectionFixed means the needle is built in (least dead space). Luer-lock screws on and cannot pop off. Luer-slip pushes on. Glossary | Fixed needle | Fixed needle |
| Needle included | Yes | Yes |
| TipBlunt tips draw liquid from a vial without being able to go through skin; they are for mixing and drawing up. | sharp | sharp |
| Dead spaceLiquid left in the hub after the plunger bottoms out. Fixed-needle insulin syringes have almost none. Glossary | low | low |
| PriceRough position within its category, not a live price: budget is the cheapest sensible option, premium costs more for a reason the page explains. | Budget | Budget |
| TravelWhether it is practical to fly with: carry-on means it goes through security without fuss. | Carry-on friendly | Carry-on friendly |
| SterileIndividually sealed and sterile until opened. Anything that touches the inside of a vial or your skin should be. | Yes | Yes |
| PackHow many you get. Check this against the photo; Amazon listings often show ten and ship one. | 100 | 100 |
| Reusable | No | No |
Which should you choose?
- Pick 31G if you draw small amounts (under 50 units) and want the finest needle; it comes on the 0.3 and 0.5 mL barrels, whose lines are easier to read.
- Pick 30G if you need the 1 mL barrel for larger draws, or if a thicker liquid draws slowly through 31G.
- Do not pick on gauge alone. Barrel size and marking increments change how accurately you can measure; gauge changes only how the needle feels.
The products
Open in the comparison tool Find the right syringe
Related guides
- Needle gauge chart: 18G to 32G, and what each is for
- 0.3, 0.5 or 1 mL insulin syringe: which size to buy
- How to read an insulin syringe
Common questions
Is 31G thinner than 30G?
Yes. Higher gauge numbers are thinner needles. 31G is one step thinner than 30G, and 32G thinner still.
Does a thinner needle hurt less?
A little, for most people; technique (room-temperature liquid, a fresh needle, slow injection) matters more than one gauge step.
Can I get 31G on a 1 mL syringe?
Rarely. Most 1 mL insulin syringes come with 29G or 30G needles; 31G is standard on the 0.3 and 0.5 mL barrels.
Reviewed 2026-09-03. Equipment comparison only; nothing here is advice about what to inject or how much. Affiliate links open your own country's Amazon store; your price is the same.