How to Convert Folate ng/mL to nmol/L
Folate (folic acid, vitamin B9) is reported in ng/mL in the US and nmol/L in most other countries. The values describe the same blood level, so converting lets you compare a result with reference ranges from either system.
The conversion factor is 2.266, from folate's molecular weight of 441.4:
Folate nmol/L = Folate ng/mL × 2.266 Folate ng/mL = Folate nmol/L ÷ 2.266 Folate ng/mL to nmol/L Chart
Reference ranges vary by laboratory; compare with the range on your own report.
| ng/mL | nmol/L | Typical status |
|---|---|---|
| 2 ng/mL | 4.5 nmol/L | Low — deficiency range |
| 3 ng/mL | 6.8 nmol/L | Lower limit of many ranges |
| 4 ng/mL | 9.1 nmol/L | Borderline-low |
| 6 ng/mL | 13.6 nmol/L | Normal |
| 10 ng/mL | 22.7 nmol/L | Comfortably normal |
| 15 ng/mL | 34.0 nmol/L | Normal |
| 20 ng/mL | 45.3 nmol/L | Upper limit of many ranges |
nmol/L to ng/mL Reverse Chart
| nmol/L | ng/mL |
|---|---|
| 7 nmol/L | 3.1 ng/mL |
| 10 nmol/L | 4.4 ng/mL |
| 20 nmol/L | 8.8 ng/mL |
| 30 nmol/L | 13.2 ng/mL |
| 45 nmol/L | 19.9 ng/mL |
Normal and Deficient Folate Ranges
Commonly cited educational bands for serum folate (they vary by lab):
| Status | Conventional (ng/mL) | SI (nmol/L) |
|---|---|---|
| Deficient | Below 3 ng/mL | Below 6.8 nmol/L |
| Borderline-low | 3–4 ng/mL | 6.8–9.1 nmol/L |
| Normal serum folate | 3–20 ng/mL | 6.8–45.3 nmol/L |
Serum Folate vs RBC Folate
There are two folate tests, and they are not interchangeable. Serum folate reflects recent intake and can rise after a single folate-rich meal, so it can look normal even when stores are low. Red blood cell (RBC) folate reflects body stores over the previous few months and is the more reliable marker of true folate status. When serum folate is borderline, clinicians often check RBC folate.
Folate, B12, and Macrocytic Anaemia
Folate and vitamin B12 deficiency both cause macrocytic (megaloblastic) anaemia, so they are tested together. Importantly, giving folate can correct the anaemia of B12 deficiency while the B12-related nerve damage keeps progressing — so B12 should be checked before treating with folate. Folate is also reviewed alongside iron studies such as ferritin when working up anaemia.
Worked Example
Suppose your folate is 3.5 ng/mL and you want nmol/L:
3.5 × 2.266 = 7.9 nmol/L 7.9 nmol/L is borderline-low, where RBC folate may be checked. For the reverse direction, 6.8 nmol/L is about 3 ng/mL, a common lower limit.
Frequently Asked Questions
How do you convert folate ng/mL to nmol/L?
Multiply ng/mL by 2.266. For example, 6 ng/mL equals about 13.6 nmol/L.
What folate level is deficient?
Below 3 ng/mL (about 6.8 nmol/L) suggests deficiency; 3–4 ng/mL is borderline-low.
Is serum folate or RBC folate better?
RBC folate reflects longer-term stores and is more reliable; serum folate can swing with recent diet.
Why check B12 with folate?
Both cause macrocytic anaemia, and folate can mask the blood signs of B12 deficiency while nerve damage continues.
References
- Medscape — Folate (Folic Acid): Reference Range (serum and RBC folate values and interpretation).
- Folate molecular weight ≈ 441.4 g/mol — SI conversion factor 1 ng/mL = 2.266 nmol/L (standard clinical laboratory unit conversion).
Conclusion
Converting folate between ng/mL and nmol/L is a simple multiply or divide by 2.266. For diagnosis, remember that RBC folate is the more reliable marker and that B12 should be checked alongside folate — interpret the result with your healthcare provider.