A1c Average Glucose
Calculator

Hemoglobin A1c measures the percentage of red blood cells that have glucose attached to them, which builds up over the roughly 2-3 month lifespan of red blood cells. This makes it a reflection of average blood sugar over the preceding two to three months rather than a single point-in-time reading.

It uses a formula derived from large clinical studies (commonly eAG = 28.7 × A1c − 46.7) that translates the A1c percentage into an estimated average glucose value in mg/dL or mmol/L, giving a number that's more intuitive to compare against daily glucose meter readings. This estimated average is a population-based conversion, not a measurement specific to your body.

Individual variation in red blood cell lifespan, certain blood disorders like anemia, and differences in how glucose binds to hemoglobin between people can cause the estimated average to diverge from what a glucose meter or continuous monitor actually shows. The formula is a useful approximation but not a perfect one-to-one conversion for everyone.

Generally, an A1c of 6.5% or higher is used to diagnose diabetes, 5.7% to 6.4% indicates prediabetes, and below 5.7% is considered normal, according to widely used clinical guidelines. These cutoffs are typically confirmed with repeat testing or additional blood glucose tests.

Not directly; because A1c reflects an average over months, it can look acceptable even if someone experiences significant post-meal glucose spikes that even out with periods of lower glucose. This is why A1c is often used alongside daily glucose monitoring rather than as the only tool for managing diabetes.