Quick answer
Both are U-100 syringes with the same 31G needle; the difference is the barrel. A 0.3 mL barrel holds 30 units and spreads them over the same length a 0.5 mL barrel uses for 50, so each unit line is further apart and easier to read. If your draws are under 30 units, the 0.3 mL is the more accurate tool. If they are ever above 30, you need the 0.5 mL.
Side by side
Rows that differ are highlighted. Values come from the product records for the two products named in the header.
0.3 mL Insulin Syringes 31G, 0.3 mL (100-count) |
0.5 mL Insulin Syringes 31G, 0.5 mL (100-count) |
|
|---|---|---|
| GaugeNeedle thickness. A higher number is a thinner needle: 31G is thinner than 30G. Glossary | 31G | 31G |
| CapacityHow much liquid the barrel holds. Smaller barrels have more space between the lines, so small amounts are easier to read. Glossary | 0.3 mL | 0.5 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 | 1 unit |
| 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 0.3 mL if every draw is under 30 units; the wider spacing is the point, and half-unit versions exist only in this size.
- Pick 0.5 mL if draws vary or go up to 50 units; one syringe covers everything without drawing twice.
- Never draw twice from a 0.3 mL to reach a larger amount; that doubles the dead-space error. Buy the size that holds the whole draw.
The products
Open in the comparison tool Find the right syringe
Related guides
- 0.3, 0.5 or 1 mL insulin syringe: which size to buy
- Insulin syringe units to mL: the quick conversion
- Measuring accurately — units, bubbles and dead space
Common questions
How many units does a 0.3 mL syringe hold?
30 units on the U-100 scale (100 units = 1 mL).
Are 0.3 mL and 0.5 mL needles the same?
Usually yes: 31G, 8 mm (5/16 in) is the common fixed needle on both.
Is there a half-unit 0.5 mL syringe?
Not commonly. Half-unit markings are a 0.3 mL feature; see the half-unit syringe in the catalogue.
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.