Understanding your thyroid test results shouldn’t be complicated. Our free TSH Unit Conversion Calculator helps you instantly convert between mIU/L and µIU/mL, the two most common units used for measuring Thyroid Stimulating Hormone levels worldwide.
TSH Unit Conversion Calculator
How to Use This TSH Converter
Using our TSH unit conversion calculator is straightforward and takes just seconds:
Step 1: Select your hormone type from the dropdown menu. TSH (Thyroid Stimulating Hormone) is pre-selected, but you can also choose T3, T4, Free T3, or Free T4 if needed.
Step 2: Choose your conversion direction. Select either “mIU/L → µIU/mL” or “µIU/mL → mIU/L” depending on which unit your lab report uses and which unit you need.
Step 3: Enter your test value in the input field. You can enter any decimal number as it appears on your lab report.
Step 4: Click the “Convert” button to see your result instantly. The calculator will display the converted value and show you the conversion formula used.
Step 5: Use the “Copy Result” button to save the converted value to your clipboard for easy sharing with your healthcare provider or for your personal records.
The “Reset” button clears all fields and returns the calculator to its default state, ready for a new conversion.
Understanding TSH Units
Thyroid Stimulating Hormone (TSH) is a hormone produced by your pituitary gland that regulates your thyroid function. TSH tells your thyroid gland how much thyroid hormone (T3 and T4) to produce. When TSH levels are too high, it typically indicates hypothyroidism (underactive thyroid). When TSH levels are too low, it usually suggests hyperthyroidism (overactive thyroid).
Doctors order TSH tests to screen for thyroid problems, monitor thyroid treatment effectiveness, and evaluate symptoms like unexplained weight changes, fatigue, or temperature sensitivity. TSH is often the first test ordered when thyroid dysfunction is suspected because it’s highly sensitive to even small changes in thyroid hormone levels.
Common TSH Measurement Units
TSH levels are measured in two primary units that are numerically identical:
mIU/L (milli-International Units per Liter) is commonly used in Europe, Asia, and many international laboratories. This unit measures the concentration of TSH in one liter of blood.
µIU/mL (micro-International Units per milliliter) is frequently used in the United States and some North American laboratories. This unit measures the concentration of TSH in one milliliter of blood.
Here’s the important part: these two units are mathematically equivalent. A TSH value of 2.5 mIU/L is exactly the same as 2.5 µIU/mL. There’s no multiplication or division needed—it’s a direct 1:1 conversion.
Why Different Labs Use Different Units
Laboratory reporting standards vary by region, country, and healthcare system. Some labs follow European standards while others follow American conventions. Additionally, different lab equipment manufacturers may default to different units. This doesn’t affect the actual measurement—only how it’s reported on your lab paperwork.
TSH Reference Ranges
Understanding normal TSH ranges helps you interpret your test results. However, remember that reference ranges can vary slightly between laboratories, and your doctor will interpret results based on your individual health situation.
| Condition | TSH Range (mIU/L or µIU/mL) | What It Means |
|---|---|---|
| Normal Range | 0.4 – 4.0 | Thyroid functioning properly |
| Subclinical Hypothyroidism | 4.5 – 10.0 | Mildly underactive thyroid |
| Hypothyroidism | > 10.0 | Significantly underactive thyroid |
| Subclinical Hyperthyroidism | 0.1 – 0.4 | Mildly overactive thyroid |
| Hyperthyroidism | < 0.1 | Significantly overactive thyroid |
Important Considerations:
Reference ranges may vary by laboratory and testing method. Always check the reference range printed on your specific lab report.
Age affects TSH levels. Older adults may have slightly higher TSH levels that are still considered normal for their age group.
Pregnancy changes TSH reference ranges. First trimester targets are typically lower (TSH < 2.5 mIU/L) to support fetal development.
Medications can influence TSH levels. Biotin supplements, thyroid medications, and certain other drugs may affect test results.
Always consult your healthcare provider for proper interpretation of your TSH results in the context of your complete medical history and symptoms.
Conversion Examples & Practice Problems
Understanding TSH Unit Conversion with Real Examples
Example 1: Basic Conversion (mIU/L to µIU/mL)
Lab Report A shows: TSH = 2.5 mIU/L
Converted to: 2.5 µIU/mL
Interpretation: This is within the normal range. Both values are identical—only the unit label changes. No mathematical calculation is needed because 1 mIU/L equals 1 µIU/mL.
Example 2: High TSH Level Conversion
Lab Report B shows: TSH = 8.7 mIU/L
Converted to: 8.7 µIU/mL
Interpretation: This is an elevated TSH level, suggesting possible subclinical hypothyroidism. The value remains 8.7 regardless of which unit is used. Your doctor would likely recommend follow-up testing or treatment.
Example 3: Low TSH Level Conversion
Lab Report C shows: TSH = 0.2 µIU/mL
Converted to: 0.2 mIU/L
Interpretation: This is a suppressed TSH level, which may indicate hyperthyroidism. Again, the numerical value stays the same—0.2 in both unit systems.
Example 4: Borderline TSH Conversion
Lab Report D shows: TSH = 4.2 mIU/L
Converted to: 4.2 µIU/mL
Interpretation: This is at the upper limit of normal. Some labs consider up to 4.5 normal, while others use 4.0 as the cutoff. Your doctor may recommend monitoring or additional testing. The conversion is still 1:1.
Example 5: Very High TSH (Overt Hypothyroidism)
Lab Report E shows: TSH = 15.3 µIU/mL
Converted to: 15.3 mIU/L
Interpretation: This significantly elevated TSH indicates overt hypothyroidism requiring treatment. Whether reported as 15.3 mIU/L or 15.3 µIU/mL, the value and clinical significance remain identical.
Practice Scenarios for Healthcare Students
Scenario 1: Comparing Two Lab Reports
A patient presents with two TSH results from different laboratories. The first result from Lab A shows 3.4 mIU/L from three months ago. The second result from Lab B shows 3.4 µIU/mL from today.
Question: Has the patient’s TSH level changed between the two tests?
Answer: No, the TSH level has remained stable at 3.4. The different units (mIU/L vs µIU/mL) do not indicate a change in the actual measurement. Both values are identical and represent the same TSH concentration.
Scenario 2: International Patient Transfer
A patient is relocating from the United States to Germany. Their most recent TSH test in the USA showed 1.8 µIU/mL. They want to know what this would be reported as in a European laboratory that uses mIU/L.
Question: What would the TSH value be reported as in Europe?
Answer: The TSH would be reported as 1.8 mIU/L in Europe. There is no numerical change—the value stays 1.8. Only the unit label changes from µIU/mL to mIU/L. The patient’s thyroid status remains the same regardless of location.
Scenario 3: Monitoring Treatment Progress
A patient was diagnosed with hypothyroidism and started on levothyroxine. Their initial TSH before treatment was 12.5 mIU/L. After six weeks of medication, a follow-up test shows TSH of 4.8 µIU/mL.
Question: Has the patient’s TSH improved with treatment?
Answer: Yes, the TSH has significantly decreased from 12.5 to 4.8, indicating the medication is working effectively. Even though the units differ (mIU/L vs µIU/mL), the values are directly comparable. The treatment has brought the TSH from a hypothyroid range down to near-normal levels.
Scenario 4: Pregnancy TSH Monitoring
A pregnant woman in her first trimester needs to maintain TSH below 2.5 mIU/L according to pregnancy guidelines. Her lab result shows TSH of 2.3 µIU/mL.
Question: Is this TSH value within the recommended target for pregnancy?
Answer: Yes, the TSH of 2.3 µIU/mL is equivalent to 2.3 mIU/L, which is below the first trimester target of 2.5. The patient’s thyroid function is adequately controlled for early pregnancy. No adjustment is needed based on this result.
Quick Reference Conversion Table
This table provides instant conversions for common TSH values you might encounter:
| mIU/L | µIU/mL | Clinical Interpretation |
|---|---|---|
| 0.1 | 0.1 | Severely suppressed (hyperthyroid range) |
| 0.4 | 0.4 | Lower limit of normal range |
| 1.0 | 1.0 | Optimal range for most adults |
| 2.5 | 2.5 | Mid-normal range, pregnancy first trimester target |
| 4.0 | 4.0 | Upper limit of normal (some labs use 4.5) |
| 5.0 | 5.0 | Mildly elevated, subclinical hypothyroidism |
| 10.0 | 10.0 | Significantly elevated, likely hypothyroidism |
| 20.0 | 20.0 | Severely elevated, definite hypothyroidism |
Common Questions About TSH Unit Conversion
Q: Are mIU/L and µIU/mL the same?
A: Yes, they are numerically equivalent. A TSH value of 1 mIU/L equals 1 µIU/mL. You can use these units interchangeably without any mathematical conversion. The only difference is how the unit is written on your lab report.
Q: Why do different labs report TSH in different units?
A: Different countries, healthcare systems, and laboratory equipment manufacturers follow varying reporting standards. European labs typically use mIU/L, while many American labs use µIU/mL. This is simply a difference in convention, not a difference in the actual measurement.
Q: How accurate is this TSH conversion calculator?
A: The calculator provides exact conversions because mIU/L and µIU/mL are mathematically equivalent units with a 1:1 ratio. There’s no rounding or approximation involved—the number you enter is the number you get out, just with a different unit label.
Q: What is a dangerous TSH level?
A: TSH above 10 mIU/L or below 0.1 mIU/L generally requires medical attention. Very high TSH (above 20) or undetectable TSH (below 0.01) can indicate severe thyroid dysfunction requiring immediate treatment. However, only your doctor can determine what’s dangerous for your specific situation.
Q: Can I use this calculator for T3 and T4 conversions?
A: This calculator handles the simple 1:1 unit conversion between mIU/L and µIU/mL, which applies to TSH. T3 and T4 hormones use different units (like ng/dL to pmol/L) that require different conversion factors. You would need a separate calculator for T3 and T4 conversions.
Q: How often should I check my TSH levels?
A: Testing frequency depends on your thyroid condition and treatment. People without thyroid problems might check TSH every few years during routine physicals. Those on thyroid medication typically test every 6-12 months once stable, or more frequently when adjusting medication doses. Always follow your healthcare provider’s recommendations.
Q: Does TSH level alone diagnose thyroid disease?
A: No, TSH is typically evaluated alongside Free T3, Free T4, thyroid antibodies, and your clinical symptoms for proper diagnosis. An abnormal TSH indicates thyroid dysfunction, but additional tests help determine the specific type of thyroid problem and guide treatment decisions.
Conclusion
Converting TSH units between mIU/L and µIU/mL doesn’t have to be confusing. As you’ve learned, these units are numerically identical—a TSH of 2.5 is 2.5 whether it’s reported as mIU/L or µIU/mL. Our free TSH Unit Conversion Calculator makes it easy to compare test results from different laboratories and understand your thyroid function tests, regardless of which unit system your lab uses.
Whether you’re monitoring hypothyroidism treatment, comparing international lab results, or simply trying to understand your thyroid health, having quick access to accurate unit conversions helps you take control of your healthcare journey. Bookmark this calculator for future use whenever you receive thyroid test results.
Remember that while this calculator helps you convert units accurately, only your healthcare provider can properly interpret your TSH results in the context of your complete medical history, symptoms, and other test findings. Always consult with your doctor about any concerns regarding your thyroid function.
Use the calculator above anytime you need instant, accurate TSH unit conversions. Share this tool with friends, family members, or anyone else who might benefit from easily converting their thyroid test results.
Medical Disclaimer: This TSH unit conversion calculator is provided for informational and educational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding thyroid function tests or medical conditions. Never disregard professional medical advice or delay seeking it because of information obtained from this calculator.