Mounjaro UK conversion to mL and units
…and why pen strength (mg) changes how many units you draw

Why this matters: In the UK, Mounjaro (tirzepatide) pens deliver a fixed 0.6 mL per injection. Syringes often show units rather than mL on a U-100 scale. The tables and examples below show how units ↔ mL ↔ mg relate for each UK pen strength, so you can understand the maths.

UK quick facts

• Dose volume per injection: 0.6 mL for all strengths
• Doses per pen: 4 per pen → total 2.4 mL per pen
• Available strengths (per dose): 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg

The three quantities: units, mL, mg

• mL is the volume of liquid.
• mg is the amount of medicine in that liquid.
• Units on a U-100 insulin syringe are just another way to show volume: 100 units = 1.00 mL.

What is a U-100 syringe?

A U-100 syringe shows volume in units where:

• 100 units = 1.00 mL
• 10 units = 0.10 mL
• 60 units = 0.60 mL

This aligns neatly with UK Mounjaro's per-injection volume of 0.6 mL.

Worked examples

Example 1: 40 units from a 5 mg UK pen

If you draw 40 units, that is 0.40 mL. A UK 5 mg pen delivers 5 mg in 0.6 mL, so 0.40 mL corresponds to about 3.33 mg. In words: forty units from a 5 mg pen gives roughly three and a third milligrams.

Example 2: aiming for about 3 mg at different strengths

From a 5 mg pen, about 3 mg is 36 units. From a 10 mg pen, about 3 mg is 18 units. Same mg, fewer units from the stronger pen.

Example 3: reading back from units to mg

If you took 24 units from a 7.5 mg pen, that is 0.24 mL. Because the 7.5 mg pen is stronger per mL, 0.24 mL equals about 3 mg.

Master conversion table (UK)

How to read this: If you want about 3 mg from a 5 mg pen, look down the 5 mg pen column. You'll see 36 units ≈ 3.000 mg and 40 units ≈ 3.333 mg. For the same ~3 mg from a 10 mg pen, the 10 mg pen column shows 18 units = 3.000 mg.

This shows why pen strength matters: stronger pens need fewer units for the same mg.

U-100 syringe; rows are units (5 → 60). "mL" is the same for all pens. Each pen column shows what that volume contains in mg for that UK strength (0.6 mL per injection).

Target dose look-up (by pen strength)

You can also read the maths this way: pick your target mg, then read across to find the units for each pen strength.

Using the same example: with a 5 mg pen and about 3 mg, the row shows 36 units. With a 10 mg pen for about 3 mg, the row shows 18 units.

*72 units exceeds 0.6 mL, which is more than one labelled UK dose volume.

Why "real-world use" can differ from the theoretical maths

The tables show pure arithmetic based on volume and strength. For example, a 5 mg pen contains about 20 mg in total, so you can calculate how many draws you'd get at a given mg.

In real-world use, the device and label rules limit that arithmetic:

• The UK pen is designed for four weekly injections of 0.6 mL each.
• Leftover liquid may remain after four doses to ensure accurate delivery, but you are instructed to discard the pen and not use any remainder.
• There is an in-use time limit after first use (for example, discard after 30 days), which can cap how much is usable from a pen.

So even if the maths suggests "more is left", the instructions for use take priority.

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