A1C Calculator - Convert A1C to Estimated Average Glucose (eAG)
This A1C calculator converts your A1C percentage into an estimated average glucose reading in mg/dL or mmol/L, or converts an average glucose meter reading into an estimated A1C. It uses the same ADA-published formula from the ADAG study, and includes a full conversion chart with mmol/mol. Free, no login.
This calculator is for education and conversion only. It does not diagnose diabetes or prediabetes and is not a substitute for a laboratory test or advice from a qualified healthcare provider. Always discuss your A1C results and treatment targets with your doctor.
What is an A1C calculator?
An A1C calculator converts a hemoglobin A1C lab result into an estimated average glucose (eAG) figure, expressed in mg/dL or mmol/L, using the formula derived from the ADAG (A1c-Derived Average Glucose) study and published by the American Diabetes Association. It can also work in reverse, turning an average glucose meter or CGM reading into an estimated A1C percentage, which helps people with diabetes understand how their day-to-day numbers relate to their next lab result.
A1C / Glucose Converter
Enter the A1C value exactly as it appears on your lab report, typically between 4.0% and 14.0%.
Sharing creates a link with your number pre-filled (e.g. ?a1c=7.0) so a friend or family member sees the same result instantly — no app, no sign-up.
What Is A1C and Why Does It Matter?
A1C, also called hemoglobin A1C or HbA1c, is a blood test that measures the percentage of hemoglobin in red blood cells that has glucose attached to it. Because red blood cells live for roughly two to three months, the A1C result reflects average blood sugar over that period rather than a single moment, which makes it the standard test for diagnosing and monitoring diabetes, according to NIDDK.
Unlike a fasting glucose test, which captures one reading at one point in time, A1C is a longer-term snapshot. This is why doctors rely on it to track how well a diabetes treatment plan is working over months, not days. The eAG conversion exists because most people are more familiar with the glucose numbers on their meter, in mg/dL or mmol/L, than with a lab percentage, so translating between the two makes A1C results easier to relate to daily readings.
What this A1C calculator computes
- Estimated average glucose (eAG): your A1C converted into the average blood sugar reading you would expect from daily testing, shown in both mg/dL and mmol/L
- A1C from average glucose: enter your average meter or CGM glucose and get an estimated A1C, useful for predicting your next lab result
- IFCC units (mmol/mol): the international unit used in many countries outside the United States, calculated alongside the percentage value
- ADA screening category: whether the entered A1C falls in the normal, prediabetes, or diabetes reference range, based on American Diabetes Association guidelines
- Full conversion chart: a side-by-side table of A1C, mg/dL, mmol/L, and mmol/mol from 5.0% to 10.0%, further down this page
How it is different from similar tools
| Tool | Primary Purpose | Key Feature |
|---|---|---|
| A1C Calculator | Convert A1C to average glucose and back, in mg/dL, mmol/L, and IFCC units | Two-way conversion with ADA category, full chart, and exact formula shown |
| Blood Glucose Calculator | Convert a single glucose reading between mg/dL and mmol/L | Unit conversion only, no A1C relationship |
| Diabetes Risk Calculator | Estimate risk of developing type 2 diabetes from lifestyle factors | Screening questionnaire, not a lab value converter |
How to Convert A1C to Average Blood Glucose
To convert A1C to estimated average glucose, multiply your A1C percentage by 28.7, then subtract 46.7. The result is your eAG in mg/dL. Divide that number by 18 to get the result in mmol/L.
Choose the conversion direction
Select A1C → Glucose if you have a lab result and want to see your estimated daily average. Select Glucose → A1C if you have meter or CGM data and want to predict your next A1C reading.
Enter your value
Type your A1C percentage exactly as it appears on your lab report, or enter your average glucose reading along with the correct unit, mg/dL or mmol/L.
Review the converted result
The calculator shows the eAG in both mg/dL and mmol/L, the IFCC equivalent in mmol/mol, and which ADA reference range the result falls into. The exact formula used is displayed below the result for transparency.
Discuss the result with your doctor
Use the converted number as a reference point in conversation with your healthcare provider, not as a replacement for clinical advice. Your doctor may adjust your personal target range based on age, pregnancy, kidney function, or other health conditions.
A1C to eAG - The Formula and a Worked Example
The eAG Formula (ADAG Study, Published by the ADA)
eAG (mg/dL) = 28.7 × A1C (%) − 46.7
Example: A1C of 7.0% → (28.7 × 7.0) − 46.7 = 200.9 − 46.7 = 154.2 mg/dL ≈ 8.6 mmol/L
This formula comes from the ADAG (A1c-Derived Average Glucose) study, which compared A1C lab results against continuous glucose monitoring data from over 500 participants to establish a reliable mathematical relationship between the two values. The ADA's own eAG/A1C conversion calculator is based on this same formula, and this page applies that published formula independently.
Step-by-step worked calculation
Step 1: Take the A1C percentage
A1C = 7.0%
Step 2: Multiply by 28.7
28.7 × 7.0 = 200.9
Step 3: Subtract 46.7
200.9 − 46.7 = 154.2 mg/dL
Step 4: Convert to mmol/L if needed
154.2 / 18 = 8.6 mmol/L
How to calculate A1C from an average glucose reading
Reverse Formula
A1C (%) = (eAG in mg/dL + 46.7) / 28.7
Example: an average glucose of 154 mg/dL → (154 + 46.7) / 28.7 = 200.7 / 28.7 = 7.0% estimated A1C
If your reading is in mmol/L, multiply it by 18 first to convert to mg/dL before applying this formula.
A1C to average blood sugar chart (eAG and mmol/mol)
| A1C (%) | eAG (mg/dL) | eAG (mmol/L) | IFCC (mmol/mol) | Category |
|---|---|---|---|---|
| 5.0% | 97 | 5.4 | 31 | Normal |
| 5.5% | 111 | 6.2 | 37 | Normal |
| 6.0% | 126 | 7.0 | 42 | Prediabetes |
| 6.5% | 140 | 7.8 | 48 | Diabetes (lower bound) |
| 7.0% | 154 | 8.6 | 53 | Diabetes |
| 7.5% | 169 | 9.4 | 58 | Diabetes |
| 8.0% | 183 | 10.2 | 64 | Diabetes |
| 8.5% | 197 | 10.9 | 69 | Diabetes |
| 9.0% | 212 | 11.8 | 75 | Diabetes |
| 9.5% | 226 | 12.6 | 80 | Diabetes |
| 10.0% | 240 | 13.4 | 86 | Diabetes |
Values rounded for reference, consistent with the ADA's published eAG conversion table. Use the calculator above for your exact A1C figure.
Converting to IFCC units (mmol/mol)
IFCC Formula
IFCC (mmol/mol) = (A1C% − 2.15) × 10.929
Example: A1C 7.0% → (7.0 − 2.15) × 10.929 = 4.85 × 10.929 = 53.0 mmol/mol
IFCC units are standard in the UK, Europe, Australia, and parts of Asia. NGSP percentage is standard in the United States.
Using Your Glucose Meter or CGM Average With This Calculator
Most glucose meters and continuous glucose monitors, including Accu-Chek, Contour, FreeStyle, and Dexcom devices, display an average glucose reading over a chosen period. Enter that average into the Glucose → A1C mode above to get an estimated A1C.
Home meters and CGM apps typically let you view an average over 7, 14, 30, or 90 days. Since A1C reflects roughly the past 90 to 120 days, weighted more toward the most recent 30 days, a longer average generally gives a closer estimate than a short-term snapshot.
- 7 or 14-day average: useful for spotting a recent trend, but tends to be the least reliable window for estimating A1C
- 30-day average: a reasonable middle ground, though still shorter than the period A1C actually reflects
- 60 to 90-day average: generally lines up most closely with an actual lab result, since it covers a similar span to A1C itself
- Device does not matter: the reverse formula only needs a single average glucose number, so it works the same whether that average comes from Accu-Chek, Contour, FreeStyle, Dexcom, or any other meter or sensor
This calculator is independent and is not affiliated with, endorsed by, or sponsored by any glucose meter or CGM manufacturer. It simply applies the published ADA eAG formula to whatever average glucose value you enter.
Real-Life Examples of Using an A1C Calculator
These scenarios show how people commonly use an A1C to glucose conversion in everyday diabetes management.
Example 1: Understanding a new lab result
Scenario: After a routine check-up, a patient receives a lab report showing an A1C of 7.0% but has no context for what that means day to day.
Calculation: eAG = (28.7 × 7.0) − 46.7 = 154.2 mg/dL, about 8.6 mmol/L.
Outcome: The patient now understands their average blood sugar has been running around 154 mg/dL over the past few months, which they can compare against their meter readings before their next doctor visit.
Example 2: Confirming a result is in the normal range
Scenario: A person with no diabetes risk factors gets an A1C of 5.4% during an annual physical and wants to understand the result.
Calculation: eAG = (28.7 × 5.4) − 46.7 = 108.2 mg/dL, about 6.0 mmol/L. Category: Normal (below 5.7%).
Outcome: The calculator confirms the A1C falls in the normal ADA reference range, giving the person a clear, friendly result they can mention to their doctor.
Example 3: Spotting a prediabetes range result early
Scenario: A routine screening test returns an A1C of 6.0%, just inside the prediabetes range.
Calculation: eAG = (28.7 × 6.0) − 46.7 = 125.5 mg/dL, about 7.0 mmol/L. Category: Prediabetes range (5.7% to 6.4%).
Outcome: Seeing the result land in the prediabetes range prompts the person to schedule a follow-up appointment and ask about lifestyle changes before the condition progresses further.
Example 4: Predicting an A1C from meter history
Scenario: Someone managing diabetes reviews their glucose meter app and sees a 90-day average of 154 mg/dL.
Calculation: A1C estimate = (154 + 46.7) / 28.7 = 7.0%.
Outcome: The person gets a reasonable preview of what their next lab result is likely to show, helping them gauge whether recent changes to diet or medication are having the intended effect before the actual test.
A1C vs Fasting Glucose vs Oral Glucose Tolerance Test
Direct Answer
A1C measures average blood sugar over roughly two to three months and does not require fasting. Fasting glucose measures a single point-in-time level after at least eight hours without food. The oral glucose tolerance test (OGTT) measures how the body processes a sugar drink over two hours and is the most sensitive test for diagnosing gestational diabetes.
| Test | Time Span Measured | Fasting Required? | Normal Range |
|---|---|---|---|
| A1C | Approximately 2-3 months | No | Below 5.7% |
| Fasting Plasma Glucose | Single moment | Yes, 8+ hours | Below 100 mg/dL |
| Oral Glucose Tolerance Test | 2-hour response window | Yes, then drink given | Below 140 mg/dL at 2 hours |
Why doctors often use more than one test
Each test has limitations. A1C can be skewed by certain blood disorders. Fasting glucose only captures one moment and can be affected by stress or illness on test day. Because of this, many doctors confirm a diabetes or prediabetes diagnosis using two different tests, or the same test on two separate days, rather than relying on a single result.
A1C, Glycemic Control, and Time in Range
Glycemic control refers to how well blood sugar is managed overall, and A1C is the most common single number used to summarize it. Time in range, a newer metric from continuous glucose monitors (CGM), shows the percentage of the day glucose stays within a target band, usually 70 to 180 mg/dL, and is increasingly used alongside A1C rather than instead of it.
A1C answers "what has my average been," while time in range answers "how stable has my day-to-day glucose actually been." Two people can share the same A1C of 7.0% with very different glycemic patterns. One person might stay close to 154 mg/dL all day, while another swings between very low and very high readings that average out to the same number. CGM-based time in range catches that variability, which A1C alone cannot show.
What A1C tells you
A single average over roughly 2-3 months. Good for long-term trend tracking and standard diagnosis criteria.
What time in range tells you
Day-to-day stability and how often glucose dips low or spikes high, captured continuously by a CGM sensor.
Most diabetes care teams now look at both. A widely cited consensus target is at least 70% time in range for many adults with type 1 or type 2 diabetes, alongside an A1C target set individually by a doctor. If you use a CGM, bring both numbers to your appointment rather than relying on A1C in isolation.
Common Mistakes When Interpreting A1C Results
These misunderstandings are common and worth knowing before drawing conclusions from an A1C number.
Treating A1C as a same-day blood sugar reading
A1C does not reflect what your glucose was this morning. It reflects an average across the past two to three months, weighted more toward the most recent 30 days. A single bad day or a single great day barely moves the number.
Expecting an exact match with meter averages
A meter or CGM average only includes the days you actually tested or wore the sensor, while A1C reflects glucose bound to red blood cells over their entire lifespan. Small differences between the two numbers are normal and expected, not necessarily an error.
Ignoring conditions that distort A1C accuracy
Anemia, recent significant blood loss, certain hemoglobin variants, and chronic kidney disease can all push A1C higher or lower than actual average glucose would suggest. People with these conditions should ask their doctor whether fasting glucose or CGM data is more reliable for them.
Self-diagnosing from a single result
A1C in the diabetes range on one test is a strong signal to see a doctor, but ADA guidelines call for confirmation with a second test on a different day, or a different test type, before a formal diagnosis is made.
Confusing NGSP percentage with IFCC mmol/mol
A lab report showing 53 is very different from one showing 5.3%. If you are comparing results from different countries, always check which unit, NGSP percentage or IFCC mmol/mol, was used before comparing numbers directly.
Assuming a short meter average predicts A1C precisely
A 7 or 14-day meter average only samples a small slice of the roughly 90 to 120-day window A1C reflects. Treat a short-term average as a rough directional signal, and use a 60 to 90-day average when you want a closer estimate.
Frequently Asked Questions
General screening reference only. Not a diagnosis.
Two-Way Conversion
A1C to glucose, or glucose to A1C
mg/dL and mmol/L
Both units shown side by side
IFCC Units
International mmol/mol included automatically
Full Conversion Chart
eAG and mmol/mol from 5.0% to 10.0% A1C
No Install Needed
Works like an app in any browser, phone or desktop
CSV Export
Download your conversion result
General ADA guidance. Your doctor sets your personal schedule.
Compare your eAG estimate against your meter or CGM average, not your highest reading
Average at least 60 to 90 days of glucose data before estimating an A1C, since shorter windows are less reliable
Mention any anemia, kidney disease, or recent blood transfusion to your doctor before relying on A1C alone
Re-test on a different day before treating one result as final
Keep a copy of your lab reports to track trends over multiple A1C tests
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