# A1C to Average Glucose Calculator

> Converts HbA1c (%) to estimated average glucose in mg/dL and mmol/L with the ADAG study equation, or an average glucose back to A1C, and reports the IFCC value in mmol/mol.

- Calculator id: `a1c-to-glucose` · Category: Medical & Clinical (`medical`) · Tool name: `convert_a1c_to_glucose`
- Canonical page: https://tttkmbb.com/medical/a1c-to-glucose · This document: https://tttkmbb.com/medical/a1c-to-glucose.md · JSON definition: https://tttkmbb.com/medical/a1c-to-glucose.json

## Purpose

Converts HbA1c (%) to estimated average glucose in mg/dL and mmol/L with the ADAG study equation, or an average glucose back to A1C, and reports the IFCC value in mmol/mol.

**Use when:** You want the average glucose implied by an A1C result, the A1C implied by an average glucose from a meter or CGM, or the NGSP-to-IFCC conversion.

**Do not use when:** Conditions alter haemoglobin glycation (haemoglobinopathies, anaemia, recent transfusion, pregnancy, kidney failure), where A1C does not track average glucose.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `direction` | enum: a1c_to_glucose \| glucose_to_a1c |  | optional, default "a1c_to_glucose" | Which quantity is being converted. |
| `value` | number |  | required | A1C in percent (NGSP) for a1c_to_glucose, or average glucose (in glucose_unit) for glucose_to_a1c. (> 0, max 1000) |
| `glucose_unit` | enum: mg_dl \| mmol_l |  | optional, default "mg_dl" | Unit of the glucose value (1 mmol/L = 18.016 mg/dL). |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `a1c_percent` | number | % | Haemoglobin A1c in NGSP/DCCT percent. |
| `a1c_mmol_mol` | number | mmol/mol | IFCC units: (A1C% − 2.15) × 10.929. |
| `eag_mg_dl` | number | mg/dL | 28.7 × A1C − 46.7. |
| `eag_mmol_l` | number | mmol/L | 1.59 × A1C − 2.59. |
| `a1c_category` | string |  | Diagnostic ranges: <5.7% normal, 5.7–6.4% prediabetes, ≥6.5% diabetes (requires confirmation). |

## Formula

`eAG (mg/dL) = 28.7 × A1C − 46.7; eAG (mmol/L) = 1.59 × A1C − 2.59; inverse: A1C = (eAG_mg_dl + 46.7) / 28.7 or (eAG_mmol_l + 2.59) / 1.59; IFCC (mmol/mol) = (A1C − 2.15) × 10.929`

The ADAG regression (Nathan 2008) has a 95% prediction interval of roughly ±30 mg/dL at an A1C of 7%, so individual eAG values are approximate. Results are informational only and not a substitute for clinical judgement or medical advice.

## Data Sources

- Nathan DM et al. (2008) Translating the A1C assay into estimated average glucose values, Diabetes Care 31:1473-1478 — https://pubmed.ncbi.nlm.nih.gov/18540046/ (peer_reviewed, retrieved 2026-09-24)
- American Diabetes Association – Diagnosis (A1C, fasting and OGTT thresholds) — https://diabetes.org/about-diabetes/diagnosis (standard, retrieved 2026-09-24)
- NGSP – IFCC/NGSP master equation — https://ngsp.org/ifccngsp.asp (standard, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/a1c-to-glucose?value=…`
- `POST https://tttkmbb.com/api/v1/calculate/a1c-to-glucose` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/a1c-to-glucose · OpenAPI operationId `convert_a1c_to_glucose` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "a1c-to-glucose", "inputs": {…}}`

## Example

- A1C 7%: inputs `{"direction":"a1c_to_glucose","value":7}` → `{"a1c_percent":7,"eag_mg_dl":154,"eag_mmol_l":8.5,"a1c_mmol_mol":53,"a1c_category":"Diabetes range (≥6.5%)"}`
- Average glucose 126 mg/dL: inputs `{"direction":"glucose_to_a1c","value":126,"glucose_unit":"mg_dl"}` → `{"a1c_percent":6,"a1c_mmol_mol":42,"a1c_category":"Prediabetes range (5.7–6.4%)"}`

```
GET https://tttkmbb.com/api/v1/calculate/a1c-to-glucose?direction=a1c_to_glucose&value=7
```

## Limitations

Conditions alter haemoglobin glycation (haemoglobinopathies, anaemia, recent transfusion, pregnancy, kidney failure), where A1C does not track average glucose. The ADAG regression (Nathan 2008) has a 95% prediction interval of roughly ±30 mg/dL at an A1C of 7%, so individual eAG values are approximate. Results are informational only and not a substitute for clinical judgement or medical advice. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Is eAG the same as my meter average?**

Roughly, if the meter average covers all times of day over about 3 months; A1C weights the most recent 4–6 weeks more heavily, and meter checks often miss post-meal peaks.

**What is the mmol/mol value?**

The IFCC unit used in the UK, Australia and much of Europe; 7% NGSP corresponds to 53 mmol/mol.

## Related

- [Glucose Unit Converter](https://tttkmbb.com/medical/glucose-unit-conversion.md) — Convert single glucose readings between units.