Important: This calculator provides an estimate, not a laboratory result or medical diagnosis. Do not use an estimated A1C to change insulin, medication, diet or another treatment without speaking with a qualified healthcare professional.

Calculate Your Estimated A1C

Calculator placement: Add the interactive calculator here, before advertisements or long explanatory content.

Average glucose

Choose your unit:

• mg/dL
• mmol/L

Enter your average blood sugar: [Input field] Button: Calculate Estimated A1C

Calculator result

Your result should display:

• Estimated A1C: [Result]%
• HbA1c: [Result] mmol/mol
• Average glucose: [Result] mg/dL
• Average glucose: [Result] mmol/L

Result warning

Your calculated A1C is an estimate based on a mathematical relationship between laboratory-measured A1C and average glucose. It cannot replace an A1C blood test and should not be used by itself to diagnose diabetes or make treatment decisions. Learn more about factors that can affect A1C accuracy.

How to Use the Average Blood Sugar to A1C Calculator

You only need an average glucose value and the correct unit.

If your glucose is measured in mg/dL

1. Select mg/dL.
2. Enter your average glucose value.
3. Select Calculate Estimated A1C.
4. Review the estimated A1C percentage and HbA1c mmol/mol result.
5. Read the accuracy warning before interpreting the number.

For example, entering an average glucose of 154 mg/dL produces an estimated A1C of approximately 7.0%.

If your glucose is measured in mmol/L

1. Select mmol/L.
2. Enter your average glucose value.
3. Select the calculation button.
4. Review the result in A1C percentage and HbA1c mmol/mol.

For example, an average glucose of 7.8 mmol/L is approximately 140 mg/dL and produces an estimated A1C of about 6.5%. Make sure you choose the correct unit. Accidentally entering an mg/dL value as mmol/L will produce an incorrect result.

What Is Estimated A1C?

A1C, also called hemoglobin A1C or HbA1c, is a blood test used to assess longer-term glucose exposure. Glucose attaches to hemoglobin inside red blood cells, and the A1C test reports the percentage of hemoglobin with glucose attached. Unlike a home glucose reading, which shows your blood sugar at one moment, a laboratory A1C result reflects glucose exposure over approximately the previous three months. The CDC explains that home readings are individual snapshots, while A1C gives a broader view of glucose levels over time. An estimated A1C from average glucose works in the opposite direction. Instead of starting with a laboratory A1C result and converting it to estimated average glucose, this calculator starts with average glucose and uses a published formula to estimate the corresponding A1C. The result is helpful for general education and for comparing glucose units. However, it is not identical to having an A1C blood test performed by a qualified laboratory.

Average Blood Sugar to A1C Formula

The calculator uses the relationship published by the American Diabetes Association: Estimated average glucose in mg/dL = 28.7 × A1C − 46.7 To estimate A1C from average glucose, the formula is rearranged: Estimated A1C = (average glucose in mg/dL + 46.7) ÷ 28.7 The ADA uses this relationship in its eAG/A1C conversion tool. The equation was developed from the A1c-Derived Average Glucose study, which compared laboratory A1C results with extensive glucose monitoring information.

Converting mmol/L to mg/dL

When a user enters glucose in mmol/L, the calculator first converts the value to mg/dL: Glucose in mg/dL = glucose in mmol/L × 18 It then applies the average glucose to A1C formula.

Converting A1C percentage to HbA1c mmol/mol

The calculator can convert the estimated A1C percentage into IFCC units with this equation: HbA1c mmol/mol = (10.93 × A1C) − 23.50 NGSP publishes the relationship between NGSP percentage and IFCC mmol/mol values. These are two reporting systems for HbA1c, so the numbers look different even when they represent a comparable result.

Average Glucose to A1C Conversion Chart

The following table shows approximate conversions. Values are rounded, so the result displayed by the calculator may differ slightly.

Average glucose mg/dL	Average glucose mmol/L	Estimated A1C	HbA1c mmol/mol
80	4.4	4.4%	25
90	5.0	4.8%	29
100	5.6	5.1%	32
110	6.1	5.5%	36
120	6.7	5.8%	40
126	7.0	6.0%	42
140	7.8	6.5%	48
154	8.6	7.0%	53
170	9.4	7.6%	59
183	10.2	8.0%	64
200	11.1	8.6%	70
212	11.8	9.0%	75
240	13.3	10.0%	86
269	14.9	11.0%	97
298	16.6	12.0%	108

The ADA and NGSP publish comparable reference values, including approximately 126 mg/dL for an A1C of 6%, 154 mg/dL for 7%, 183 mg/dL for 8% and 212 mg/dL for 9%.

Average Blood Sugar to A1C Examples

Example 1: Average glucose of 100 mg/dL

Calculation: (100 + 46.7) ÷ 28.7 = 5.11 Estimated result:

• A1C: approximately 1%
• HbA1c: approximately 32 mmol/mol
• Average glucose: 6 mmol/L

This does not prove that a laboratory A1C test would return exactly 5.1%.

Example 2: Average glucose of 140 mg/dL

Calculation: (140 + 46.7) ÷ 28.7 = 6.51 Estimated result:

• A1C: approximately 5%
• HbA1c: approximately 48 mmol/mol
• Average glucose: approximately 8 mmol/L

An estimated result at a diagnostic threshold should not be treated as a diagnosis. Diagnostic decisions require appropriate testing and professional interpretation.

Example 3: Average glucose of 154 mg/dL

Calculation: (154 + 46.7) ÷ 28.7 = 6.99 Estimated result:

• A1C: approximately 0%
• HbA1c: approximately 53 mmol/mol
• Average glucose: approximately 6 mmol/L

Example 4: Average glucose of 200 mg/dL

Calculation: (200 + 46.7) ÷ 28.7 = 8.60 Estimated result:

• A1C: approximately 6%
• HbA1c: approximately 70 mmol/mol
• Average glucose: approximately 1 mmol/L

A high calculated value should be discussed with a healthcare professional, especially when it is supported by repeated high glucose readings or symptoms.

Why a Few Finger-Prick Readings May Not Predict A1C Reliably

One of the most important limitations of a glucose to A1C calculator is the quality of the average entered. A home glucose meter reading represents one point in time. Blood sugar can change after meals, exercise, medication, stress, illness, sleep and other daily events. The CDC notes that individual home readings do not provide the same complete picture as an A1C test. For example, someone might test only:

• Before breakfast
• Before eating
• When they expect a normal result
• On a few days each month

That average may miss:

• After-meal spikes
• Overnight highs
• Early-morning changes
• Periods of low blood sugar
• Days when glucose was unusually high
• Variability between weekdays and weekends

Averaging five or ten convenient readings is therefore not the same as measuring glucose continuously across several weeks.

A better input value

A more representative average may come from:

• A continuous glucose monitor covering a meaningful period
• A meter download containing readings from different times of day
• A structured testing schedule prescribed by a healthcare professional
• A large collection of readings covering meals, fasting periods and bedtime

Even with more data, the calculated value remains an estimate and may not match a laboratory test.

Why Your Estimated A1C May Not Match Your Laboratory A1C

A difference between calculated A1C and measured A1C does not automatically mean that your meter or laboratory result is wrong.

1. Your readings may not cover the entire day

Finger-prick readings can miss glucose changes between tests. If you mostly test while fasting, your calculated average may not capture after-meal increases.

2. The number of readings may be too small

A few readings cannot reliably represent every hour across two or three months.

3. Recent glucose changes can affect the comparison

A1C reflects a longer period, but glucose during the most recent month can have a greater influence on the result than glucose from earlier months. If your glucose improved only recently, your current meter average may look lower than the laboratory A1C.

4. Red-blood-cell lifespan varies

A1C depends partly on how long red blood cells remain in circulation. Conditions that shorten or extend their lifespan may change an A1C result independently of the average shown by a glucose meter.

5. Medical conditions can affect A1C

NIDDK identifies several circumstances that can affect A1C, including recent blood loss, blood transfusion, sickle cell disease, erythropoietin treatment, hemodialysis, iron-deficiency anemia, kidney failure, liver disease and some hemoglobin variants. The CDC also lists severe anemia, certain blood disorders, pregnancy and some medicines among factors that may falsely increase or decrease an A1C result. Read the complete guide to A1C calculator limitations and factors that affect A1C.

6. Glucose devices have measurement limitations

Home glucose meters and continuous glucose monitors are useful tools, but their readings can vary because of device performance, sensor conditions, testing technique and timing.

7. A1C laboratory measurements also have variation

NIDDK explains that repeat A1C measurements can be slightly higher or lower, even when testing the same blood sample.

Can This Calculator Diagnose Diabetes or Prediabetes?

No. A calculated A1C cannot diagnose diabetes or prediabetes. The commonly used laboratory A1C diagnostic ranges are:

Laboratory A1C result	General diagnostic category
Below 5.7%	Normal range
5.7% to 6.4%	Prediabetes range
6.5% or higher	Diabetes range

These categories apply to appropriately performed A1C testing, not an estimate created from home glucose readings. The CDC publishes these general laboratory ranges and advises people to discuss testing and results with a healthcare professional. Do not label the calculator output as “normal,” “prediabetes” or “diabetes” without a prominent explanation that it is not diagnostic. A safer result message is: This estimated value falls near a range commonly used when interpreting laboratory A1C tests. However, a calculation from average glucose cannot diagnose any condition. Ask a healthcare professional whether laboratory testing is appropriate.

Practical Tips for a More Useful Estimate

Use more than a few readings

A larger number of readings taken at different times generally provides a more representative average than a few fasting values.

Include different times of day

Your data may be more useful when it includes readings:

• After waking
• Before meals
• After meals
• Before bed
• During symptoms
• During exercise or illness when advised

Follow the monitoring schedule recommended by your healthcare professional.

Do not remove unusual readings just to improve the average

High and low values may be meaningful. Removing them without a valid reason can produce a misleading estimate.

Check the unit before calculating

US glucose meters commonly report mg/dL. Many other countries use mmol/L. Examples:

• 100 mg/dL is approximately 6 mmol/L
• 140 mg/dL is approximately 8 mmol/L
• 180 mg/dL is approximately 0 mmol/L

Do not use the result for insulin dosing

The average blood sugar to A1C calculator is not an insulin-dose calculator. It does not account for current glucose, carbohydrate intake, insulin sensitivity, active insulin, illness or individual treatment instructions.

Compare it with your next laboratory result

When you receive a laboratory A1C result, compare it with your previous estimate. A substantial or repeated difference is worth discussing with a healthcare professional.

When Should You Speak With a Healthcare Professional?

Consider contacting a qualified healthcare professional when:

• Your glucose readings are repeatedly outside your recommended range.
• Your calculated A1C is much higher or lower than expected.
• Your laboratory A1C does not match your meter or CGM data.
• You experience frequent high or low readings.
• You have symptoms that concern you.
• You are pregnant or planning pregnancy.
• You have anemia, kidney disease, liver disease or a known blood disorder.
• You recently had major blood loss or a blood transfusion.
• You are considering changing medication, insulin or another treatment.

Seek urgent medical assistance for severe symptoms or an emergency rather than relying on an online calculator.

Medical Disclaimer

This calculator and page are provided for general educational purposes only. They are not medical advice, diagnosis or treatment. The estimated A1C result may differ from a laboratory-measured result. Do not use this calculator to start, stop or change medication, insulin, diet or another treatment. Discuss glucose readings, A1C testing and personal targets with a qualified healthcare professional who understands your medical history.