What Is a Normal Blood Sugar Level? A Plain-English Guide for People in the UK

Blood sugar levels are one of the most commonly measured health indicators in the UK, yet many people are unclear about what the numbers actually mean. If you have recently had a blood test and your doctor mentioned glucose levels, if you have been told you are at risk of diabetes, or if you have just started home monitoring, this guide aims to give you a clear and practical understanding of what is normal and what warrants attention.

What Is Blood Sugar and Why Does It Matter?

Blood glucose is the primary fuel your body uses for energy, derived mainly from carbohydrates. After a meal, blood glucose rises. The pancreas responds by releasing insulin, which allows cells to absorb glucose and brings levels back down. When this system does not work well, blood sugar remains elevated, causing cumulative damage to blood vessels, nerves, and organs — the basis of diabetes and its complications.

Read our blog on the early signs of diabetes and on type 2 diabetes — symptoms, diagnosis, and management for further background.

How Is Blood Sugar Measured in the UK?

In the UK, blood glucose is measured in millimoles per litre (mmol/L). The main methods are:

• Fasting blood glucose: Taken after at least eight hours without food.
• Random blood glucose: Taken at any time regardless of when you last ate.
• HbA1c (glycated haemoglobin): Reflects average blood sugar over the previous two to three months. The most widely used test for diagnosing and monitoring diabetes.

Home testing devices such as the Freestyle Libre 2 provide real-time continuous glucose readings. See also the Freestyle Libre sensor range available at Pharmacy Planet, as well as a wide range of blood glucose test strips.

Normal Blood Sugar Levels in the UK

Fasting Blood Glucose

• Normal: 3.9 to 5.4 mmol/L
• Pre-diabetes: 5.5 to 6.9 mmol/L
• Diabetes: 7.0 mmol/L or above on two separate occasions

Two Hours After Eating

• Normal: Below 7.8 mmol/L
• Pre-diabetes: 7.8 to 11.0 mmol/L
• Diabetes: 11.1 mmol/L or above

HbA1c Levels

• Normal: Below 42 mmol/mol (below 6.0%)
• Pre-diabetes: 42 to 47 mmol/mol (6.0% to 6.4%)
• Diabetes: 48 mmol/mol or above (6.5% or above)

These reference ranges align with NICE and WHO guidance. Results should always be interpreted by your GP in the context of your overall health.

What Is Pre-Diabetes and Should You Be Worried?

Pre-diabetes means your blood sugar is higher than normal but not yet at diabetic levels. Lifestyle changes — losing 5–10% of body weight, increasing physical activity, and improving diet — can reduce the risk of progression by up to 58%. Read our blog on tips to prevent and control diabetes for practical guidance.

What Causes Blood Sugar to Rise?

• Food and drink, particularly refined carbohydrates and sugary foods
• Physical activity (exercise generally lowers blood sugar)
• Stress (cortisol raises blood sugar) — read our blog on how stress impacts blood sugar and ways to manage it
• Illness (infection and inflammation raise blood sugar)
• Certain medications including steroids and some antipsychotics

Home Blood Sugar Monitoring

The Freestyle Libre 2 and other continuous glucose monitors are particularly useful for understanding how diet, activity, and medication affect your blood sugar throughout the day. Read the step-by-step guide on how to use Freestyle Libre 3 and our blog on how to perform a blood glucose test at home.

Frequently Asked Questions

What is a dangerously high blood sugar level?

Above 13.9 mmol/L is significantly elevated and may indicate poor diabetes control. Above 27.8 mmol/L carries a risk of diabetic ketoacidosis (DKA) or hyperosmolar hyperglycaemic state (HHS), both requiring urgent medical attention.

What is a low blood sugar (hypoglycaemia)?

Below 4.0 mmol/L is generally considered low. Below 3.5 mmol/L is significantly low and may cause shakiness, sweating, and confusion. Hypoglycaemia is most common in people taking insulin or certain diabetes medications.

Does eating sugar cause diabetes?

Eating sugar alone does not cause diabetes. However, a diet high in refined carbohydrates can contribute to obesity, which is the single biggest modifiable risk factor for type 2 diabetes. Read our blog on a type 2 diabetes diet and balanced meal planning.

Where can I buy glucose monitoring equipment?

Pharmacy Planet stocks the Freestyle Libre sensor range, Freestyle Libre 2 sensors, the Dexcom One, and a wide range of test strips.

Reviewed for clinical accuracy. Content is for informational purposes only and does not constitute medical advice. All prescription medicines require a valid prescription following appropriate clinical assessment.