How do I calculate HOMA-IR when my insulin is in µU/mL or pmol/L
HOMA-IR is fasting glucose in mg/dL times fasting insulin in µU/mL divided by 405. If insulin is in pmol/L, divide by 6.0 to get µU/mL, or use (glucose mmol/L × insulin pmol/L) ÷ 135 when glucose is also mmol/L.
HOMA-IR is fasting glucose in mg/dL times fasting insulin in µU/mL divided by 405. If insulin is in pmol/L, divide by 6.0 to get µU/mL, or use (glucose mmol/L × insulin pmol/L) ÷ 135 when glucose is also mmol/L. The base formula was described by Matthews et al., 'Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man,' Diabetologia, 1985. The original fasting glucose-insulin HOMA formula and unit constants come from that paper.
HOMA-IR = (fasting glucose in mg/dL × fasting insulin in µU/mL) ÷ 405
Some reports write µIU/mL instead of µU/mL; they are the same thing.
Conversions:
- Insulin in pmol/L to µU/mL: divide by 6.0. This 6.0 factor is a conventional approximation. If your lab report prints a different conversion factor, use that factor instead.
- Insulin in mU/L is the same number as µU/mL, so 12 mU/L is 12 µU/mL.
- Glucose in mmol/L to mg/dL: multiply by 18.0. A value of 5.2 mmol/L becomes 93.6 mg/dL.
Formula paths:
- Glucose in mg/dL and insulin in µU/mL:
(glucose × insulin) ÷ 405. - Glucose in mmol/L and insulin in µU/mL:
(glucose × insulin) ÷ 22.5. - Glucose in mmol/L and insulin in pmol/L:
(glucose × insulin) ÷ 135.
The 22.5 and 135 shortcuts come from collapsing the conversions into the 405 constant. If your lab uses a different factor for pmol/L to µU/mL, do not use the 22.5 or 135 shortcuts without recalculation.
The free HealthOS HOMA-IR calculator at https://healthosx.com/blood/homa-ir uses the live formula with glucose in mg/dL and insulin in µIU/mL (same as µU/mL). Convert pmol/L to µU/mL first.
A worked example with both unit systems
Take a fasting glucose of 5.2 mmol/L and a fasting insulin of 72 pmol/L.
- 1.Convert glucose: 5.2 × 18.0 = 93.6 mg/dL.
- 2.Convert insulin: 72 ÷ 6.0 = 12 µU/mL.
- 3.Apply the formula: 93.6 × 12 ÷ 405 = 2.77.
The SI shortcut gives the same result: 5.2 × 72 ÷ 135 = 2.77.
What HOMA-IR is actually measuring
HOMA-IR is a steady-state model, not a direct measurement. As a simplified explanation of the original model: when fasting glucose is stable, a higher fasting insulin for the same glucose level indicates more insulin resistance. The formula multiplies glucose and insulin because the product captures both the glucose level the body is trying to hold and the hormonal effort required to hold it. The 405 denominator is the original scaling constant described by Matthews et al. Cutoffs are assay- and population-dependent.
This is not the same as a clamp study, which measures glucose disposal directly. HOMA-IR is an inexpensive fasting approximation, and it performs best when beta cells are still able to raise insulin in response to resistance.
What is a normal HOMA-IR, and what cutoffs should you use?
There is no universal cutoff. The number is influenced by age, sex, ethnicity and the specific insulin assay. Reference intervals can vary by laboratory and population. Children and adolescents need age-specific reference ranges.
If your report prints a range, use that first. A value above it is a pointer, not a diagnosis.
Use a fasting sample
HOMA-IR assumes fasting glucose and insulin. If the draw was not truly fasted, the steady-state assumption behind the formula does not hold. Do not interpret a nonfasted HOMA-IR. Repeat it before making any decision.
When HOMA-IR is not the right tool
HOMA-IR is less reliable in type 1 diabetes, advanced type 2 diabetes, and people using injected insulin. The model assumes a pancreas that can still raise insulin output when resistance increases. In beta cell failure, the insulin number stays low even though resistance is high, so the formula underestimates resistance.
Acute infection, surgery, severe sleep loss or steroid medication can also push fasting glucose and insulin around independently of true insulin resistance. If your result does not match how you feel, retest before overreacting.
What to do next
Take a persistently high HOMA-IR or abnormal fasting glucose or insulin to a doctor. The fasted HOMA-IR number is most useful next to the rest of your fasting metabolic panel. Upload your lab PDF or photo at https://healthosx.com/blood to see every marker explained against ranges for your age and sex. If earlier reports are already stored in your own browser, up to 12 reports, a new upload can then show movement since those reports.
Written by
HealthOS Research