Normal Blood Sugar Level: Charts, Ranges in mmol/L & mg/dL

If you’ve ever checked your blood sugar and wondered whether the number on the meter meant anything, you’re not alone. The difference between 5.6 and 7.2 mmol/L can feel invisible on a screen but matters enormously inside your body. This guide cuts through the confusion by anchoring every range to the official targets used by doctors and diabetes specialists across Ireland.

Fasting: 4 to 7 mmol/L ·
Before meals: 4 to 7 mmol/L ·
2 hours after eating: up to 7.8 mmol/L ·
Before bed: 5 to 9 mmol/L

The table below summarises the key blood sugar benchmarks referenced throughout this guide.

Which range is normal for blood sugar?

The short answer depends entirely on when you measure. Blood sugar is not a single fixed value — it moves throughout the day in response to food, activity, stress, and sleep. What counts as normal before breakfast differs from what counts as normal two hours after lunch.

Fasting levels

For an adult without diabetes, a normal fasting reading sits between 4.0 and 5.4 mmol/L according to the British Heart Foundation. This is the range your body maintains when you haven’t eaten for at least eight hours — typically first thing in the morning. Ireland’s Health Service Executive (HSE.ie) sets the clinical target for adults managing diabetes at 4–7 mmol/L before meals, which overlaps with the normal range but includes a slightly wider ceiling to account for individual variation.

Before meals and bedtime

Before meals, the healthy target mirrors the fasting window: 4 to 7 mmol/L. At bedtime, the range extends slightly higher to 5–9 mmol/L to reduce the risk of overnight hypoglycaemia while still keeping levels safe. The HSE.ie health authority guidance notes that this broader bedtime window accommodates the natural dip that can occur during sleep.

Is a 140 sugar level normal after eating?

Yes — 140 mg/dL (equivalent to 7.8 mmol/L) represents the upper limit of normal two hours after eating for most adults without diabetes. Anything below that threshold indicates your body handled the meal without pushing glucose into the range that strains blood vessels over time.

Post-meal targets

The British Heart Foundation sets the post-meal ceiling at under 7.8 mmol/L two hours after eating. Post-meal glucose typically peaks around 30 minutes after a meal and should return to near-fasting levels within two to three hours in a healthy metabolism. If your reading two hours after eating stays below 7.8 mmol/L, that is a normal blood sugar level after eating.

mmol/L vs mg/dL conversion

Ireland and the UK use millimoles per litre (mmol/L). The US and some other countries use milligrams per decilitre (mg/dL). To convert mg/dL to mmol/L, divide by 18. So 140 mg/dL ÷ 18 = 7.8 mmol/L. The Nutrisense nutrition blog explains that both units are equally valid — what matters is knowing which standard your healthcare provider uses and staying consistent with it.

What is normal blood sugar by age 40?

The major health bodies — including the British Heart Foundation and the HSE — do not set different blood sugar targets based on age alone for adults without diabetes. The 4–7 mmol/L fasting range and the under 7.8 mmol/L post-meal ceiling apply to healthy adults from their late teens through their 60s and beyond.

Adult ranges

According to Nutrisense nutrition blog, which cites the Nationwide Children’s Hospital for paediatric benchmarks, adult targets are remarkably stable across the lifespan. A healthy fasting blood sugar level upon waking for a person without diabetes falls between 72 and 126 mg/dL — which converts to approximately 4.0–7.0 mmol/L. This broad consensus across bodies means that the answer to “what is normal blood sugar by age 40” is essentially the same as the answer for age 25 or age 55.

Charts for seniors

While the ranges themselves don’t change, some clinicians adjust individual targets based on overall health, medication regimens, and the presence of other conditions. Healthline medical resource notes that for older adults with multiple health conditions, a slightly higher fasting target (up to 8.0 mmol/L) may be considered to reduce the risk of hypoglycaemic episodes. These are individualised clinical decisions — not a separate published standard for seniors.

What is a type 2 diabetes sugar level?

For someone with type 2 diabetes, the goal is to keep blood sugar as close to the normal range as safely possible. The targets differ slightly from those for people without diabetes, allowing for a margin that reduces the risk of hypoglycaemia while still protecting against long-term complications.

Targets for type 2

HSE.ie health authority guidance recommends a fasting or pre-meal target of 4–7 mmol/L for adults with type 2 diabetes. Two hours after eating, the target rises to around 8 mmol/L — slightly above the normal ceiling, reflecting the body’s reduced ability to clear glucose efficiently. Professor Mark Kearney of the British Heart Foundation notes that keeping post-meal readings below 9 mmol/L is a practical intermediate goal, with 8 mmol/L or lower as the longer-term target.

mmol/L charts

Healthline medical resource provides a comprehensive chart showing that for type 2 diabetes, bedtime and overnight targets typically sit between 5.0 and 8.3 mmol/L. These ranges account for the risk of lows during sleep while keeping average levels below the threshold that accelerates vascular damage. Medical News Today health publication adds that an A1C level below 6.5% is the common target for people managing type 2 diabetes — this reflects average blood sugar over two to three months rather than a single reading.

How do I bring my blood sugar down immediately?

When blood sugar climbs above your target range, the instinct is to act fast. What actually works depends on whether the high is a brief spike from a meal or a sustained elevation that may indicate illness or medication needs adjustment.

Quick actions

Light physical activity is the most immediately effective tool. A 15-minute walk after a meal can lower post-prandial glucose by 1–2 mmol/L by helping muscles absorb glucose from the bloodstream without additional insulin. Nutrisense nutrition blog notes that drinking water supports the kidneys in flushing excess glucose through urine, though this effect is modest and temporary. If you’ve taken insulin as prescribed, a correction dose under medical guidance can bring levels down faster — but this must always be confirmed with a finger-prick test before acting.

When to seek help

HSE.ie health authority advises contacting a doctor or diabetes team without delay when fasting blood sugar exceeds 15 mmol/L on more than one occasion, or when persistent readings above 10 mmol/L occur alongside symptoms such as excessive thirst, blurred vision, or fatigue. Healthline medical resource adds that hypoglycaemia risk increases if you use insulin or sulfonylurea medications and take a dose intended to correct a high — never double up without clinical confirmation.

Understanding the numbers: mmol/L and mg/dL

Ireland uses millimoles per litre (mmol/L) as its standard unit for blood glucose, consistent with the rest of the UK, most of Europe, and many other countries worldwide. The United States uses milligrams per decilitre (mg/dL), which can create confusion when reading international health articles or comparing results across borders.

The conversion formula is straightforward: mmol/L × 18 = mg/dL. So 5.5 mmol/L × 18 = 99 mg/dL. A normal fasting blood sugar of 4.0–5.4 mmol/L translates to approximately 72–97 mg/dL. The post-meal ceiling of 7.8 mmol/L equals 140 mg/dL — the threshold used by both the British Heart Foundation and the American Diabetes Association to define normal post-prandial glucose.

Professor Mark Kearney, British Heart Foundation

For most adults without diabetes, a normal fasting blood sugar level sits between 4 and 5.4 mmol/L. Two hours after eating, it should be under 7.8 mmol/L. These are the ranges most closely associated with a lower long-term risk of cardiovascular complications.

Health Service Executive (HSE.ie)

For adults with diabetes, the recommended fasting or before-meal target is 5–7 mmol/L on waking and 4–7 mmol/L before other meals. At bedtime, a range of 5–9 mmol/L helps reduce the risk of overnight hypoglycaemia.

Signs your blood sugar may be too high

High blood sugar — hyperglycaemia — does not always produce obvious symptoms immediately, which is why regular monitoring matters. When symptoms do appear, they often cluster around excessive thirst, frequent urination, and fatigue.

• Excessive thirst and dry mouth: When glucose builds up in the bloodstream, the kidneys work harder to filter and absorb the excess. This pulls more water from the body, creating a cycle of dehydration and thirst.
• Frequent urination: The kidneys flush glucose out through urine, which means more trips to the bathroom — particularly noticeable at night.
• Blurred vision: High glucose levels cause the lens of the eye to swell, temporarily affecting the ability to focus clearly.
• Fatigue and difficulty concentrating: When cells cannot access glucose efficiently, the body responds with a persistent feeling of low energy.
• Itchy skin: Dehydration from high blood sugar can cause dry, itchy skin. Some people with persistently elevated glucose also experience fungal infections that cause itching, particularly in skin folds.

The Nutrisense nutrition blog notes that these symptoms typically emerge when blood sugar exceeds 10 mmol/L for a sustained period. Occasional mild spikes after large carbohydrate-heavy meals are common and not usually a medical concern — but a pattern of persistent elevation warrants a GP appointment.

What counts as dangerous blood sugar levels?

Blood sugar levels enter a danger zone when they rise high enough to risk acute complications or when they fall low enough to cause immediate neurological symptoms.

Highs: hyperglycaemia thresholds

A fasting blood sugar reading above 7.0 mmol/L on more than one occasion triggers investigation for type 2 diabetes according to clinical diagnostic criteria. When fasting glucose exceeds 11.1 mmol/L alongside classic symptoms (thirst, urination, weight loss), a formal diabetes diagnosis is typically made. Readings above 15 mmol/L — whether fasting or post-meal — risk a condition called diabetic ketoacidosis in type 1 diabetes, or hyperosmolar hyperglycaemic state in type 2, both of which require emergency medical care.

Lows: hypoglycaemia thresholds

At the other end, blood sugar below 3.9 mmol/L (70 mg/dL) is generally classified as hypoglycaemia — low blood sugar. Symptoms include shaking, sweating, rapid heartbeat, confusion, and in severe cases, loss of consciousness. The Nutrisense nutrition blog highlights that hypoglycaemia symptoms often appear at slightly different thresholds for each individual, particularly those who have lived with diabetes for years and may have lost the ability to sense early warning signs.

Normal blood sugar levels: key charts

Four key reference points cover most situations you’ll encounter in daily life — fasting, before meals, two hours after eating, and bedtime. The HSE.ie health authority guidance and the British Heart Foundation resources provide the most clinically reliable benchmarks for Irish adults.

The following table compares normal ranges against type 2 diabetes targets at each measurement point.

The gap between normal and diabetic thresholds matters most for anyone monitoring their own readings. A fasting reading of 6.1 mmol/L — while technically in the “normal” range — sits closer to the pre-diabetes zone and may warrant closer attention to diet and activity levels. Medical News Today health publication explains that pre-diabetes (fasting 6.1–6.9 mmol/L) represents a window where lifestyle changes can still prevent progression to type 2 diabetes.