Convert IU/L to mIU/mL for TSH, hCG, LH, FSH, prolactin, insulin, and erythropoietin, with the numeric value staying the same for lab tests.
Quick Overview
When labs report hormones or similar assays in IU/L, the same result can be written as mIU/mL without changing the number.
- 1 IU = 1000 mIU
- 1 L = 1000 mL
- 1 IU/L = 1 mIU/mL
- 5 IU/L = 5 mIU/mL
- 10 IU/L = 10 mIU/mL
This identity is commonly used for tests such as TSH, hCG, LH, FSH, prolactin, insulin, and erythropoietin.
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IU/L to mIU/mL Formula
Converting IU/L to mIU/mL does not change the number. Both units describe the same concentration, so the value you put in is the value you get back:
mIU/mL = IU/L
This holds because the top and bottom of the ratio each scale by 1000. One international unit contains 1000 milli-international units, and one liter contains 1000 milliliters, so the two factors of 1000 cancel:
1 IU/L = (1 IU x 1000) / (1 L x 1000) = 1000 mIU / 1000 mL = 1 mIU/mL
For the other units in the calculator, multiply the value in IU/L by a fixed factor:
Value(target) = Value(IU/L) x Factor
Variables:
- IU/L is the concentration in international units per liter
- mIU/mL is the concentration in milli-international units per milliliter, which is equal to IU/L
- Factor is the multiplier for the unit you want: 1 for mIU/mL, 0.001 for IU/mL, and 1000 for mIU/L or uIU/mL
Pick what you want to find at the top of the calculator. The default mode takes a value in IU/L and returns mIU/mL, and the second mode reverses it. Both give the same number because the units are equal. The third mode converts between IU/L, mIU/mL, IU/mL, mIU/L, and uIU/mL, which helps when a result is reported in a unit your reference range does not use. Every result also lists the value in all five units so you can read across to whichever one you need.
Unit Equivalents for Hormone Lab Values
The first table shows how one value in IU/L is written in the other units. Read across any row to find the matching number.
| IU/L | mIU/mL | IU/mL | mIU/L (= uIU/mL) |
|---|---|---|---|
| 1 | 1 | 0.001 | 1,000 |
| 2.5 | 2.5 | 0.0025 | 2,500 |
| 5 | 5 | 0.005 | 5,000 |
| 10 | 10 | 0.01 | 10,000 |
| 25 | 25 | 0.025 | 25,000 |
| 100 | 100 | 0.1 | 100,000 |
The second table lists the units that common blood tests are usually reported in, so you can see when the IU/L and mIU/mL identity applies.
| Test | Usual unit | Same value as |
|---|---|---|
| FSH (follicle stimulating hormone) | mIU/mL | IU/L |
| LH (luteinizing hormone) | mIU/mL | IU/L |
| hCG (pregnancy) | mIU/mL | IU/L |
| TSH (thyroid) | uIU/mL | mIU/L |
| Insulin | uIU/mL | mIU/L |
Example Problems
Example 1: Convert IU/L to mIU/mL.
An FSH result reads 5 IU/L and the chart you are using is in mIU/mL. Because the units are equal, no math is needed:
5 IU/L = 5 mIU/mL.
Example 2: Convert IU/L to uIU/mL.
A result of 25 IU/L needs to be written in uIU/mL. Multiply by 1000:
25 x 1000 = 25,000 uIU/mL. The same value in IU/mL is 25 / 1000 = 0.025 IU/mL.
Frequently Asked Questions
Is IU/L the same as mIU/mL?
Yes. A value in IU/L and the same value in mIU/mL are identical. Changing IU to mIU multiplies by 1000, and changing L to mL divides by 1000, so the two changes cancel. A result of 12.4 IU/L is 12.4 mIU/mL, with no rounding or adjustment.
How do you convert mIU/mL back to IU/L?
Use the same number. Since the units are equal, going from mIU/mL to IU/L also leaves the value unchanged, so 8 mIU/mL is 8 IU/L. This is why lab reports and reference ranges can switch between the two labels without recalculating anything.
What about uIU/mL and mIU/L?
These two units are equal to each other, and both are 1000 times smaller than IU/L. One IU/L equals 1000 uIU/mL, so to go from IU/L to uIU/mL you multiply by 1000, and to go back you divide by 1000. TSH and insulin are the tests most often reported in uIU/mL.
