0.3 mL vs 0.5 mL insulin syringes: which size?
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) |
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|---|---|---|
| GaugeGauge is the needle's thickness. A higher number is a thinner needle: 31G is thinner than 30G. Glossary | 31G | 31G |
| CapacityCapacity is how 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 |
| MarkingsMarkings are the scale printed on the barrel. U-100 means 100 units to the millilitre, so one unit is 0.01 mL; a mL scale is marked in tenths or fifths of a millilitre, depending on the barrel. Glossary | U-100 | U-100 |
| Smallest lineSmallest line is what 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 lengthNeedle length is how long the needle is. 4–8 mm (5/32–5/16 in) is common for under-the-skin use, and 13 mm (1/2 in) insulin syringes are used under the skin too; muscle needles are usually 25 mm (1 in) or longer. Glossary | 8 mm | 8 mm |
| Needle connectionNeedle connection is how the needle attaches. Fixed means it is built in (least dead space). Luer-lock screws on and cannot pop off. Luer-slip pushes on. None means there is no luer fitting at all — a pen needle screws onto the pen's own thread. Glossary | Fixed needle | Fixed needle |
| Needle included | Yes | Yes |
| TipTip is the shape of the needle's point. A blunt tip is far less likely to stick you while mixing and drawing up, but it is still a sharp that can go through skin under force. Never for injecting. | Sharp | Sharp |
| Dead spaceDead space is the liquid left in the hub after the plunger bottoms out. Fixed-needle insulin syringes have almost none. Glossary | Low | Low |
| PricePrice tier is the rough 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 |
| TravelTravel says whether it is practical to fly with: carry-on means it goes through security without fuss. | Carry-on friendly | Carry-on friendly |
| SterileSterile means individually sealed and sterile until opened; anything that touches the inside of a vial or your skin should be. | Yes | Yes |
| PackPack is how many come in the listing this site links to; it is shown only where every store's listing gives the same count. Check it against the listing, since photos 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 are commonest 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: conversion chart
- 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.
Last edited . Equipment only: nothing on this page is advice about what to inject, how much, or whether a product is fit to use. That comes from the product's labelling and whoever supplied it. Product pages link to your own country's Amazon store through affiliate links; your price is the same.