DEXA scan vs smart scale: what each measures, what it costs and how far to trust it

What does a DEXA scan measure?

DEXA (also written DXA) is a scan that uses low-dose X-rays. The NHS describes it as a way of seeing how dense, or strong, your bones are.¹ In everyday talk, though, people also use “DEXA” for the whole-body scan offered privately to measure body fat and muscle.

A review of DEXA body composition splits the body into three parts: bone mineral, fat, and soft tissue without fat, usually called lean mass.⁶ Lean mass is not the same as muscle. It includes water, minerals in soft tissue and protein.⁶ The same review says MRI and CT are regarded as the reference techniques for muscle mass, because DEXA measures a chemical compartment, not an anatomical one.⁶

There is a second limit. In the part of the image that covers bone, which the review puts at 40 to 45% of the scan area, DEXA can only tell bone from soft tissue as a whole.⁶ And the result moves with hydration and with what you have eaten: meals are linked to higher lean mass readings in the trunk and the whole body.⁶ The review says the most reproducible conditions are a scan after an overnight fast.⁶

For the wider picture of fat, muscle and bone, see what body composition is.

DEXA versus a smart scale: side by side

A smart scale does something quite different. The British Heart Foundation explains that these scales send tiny electrical impulses through the body to estimate fat.¹⁰ This is bioelectrical impedance analysis, or BIA. It estimates lean mass from prediction equations, and those equations rest on assumptions about hydration.¹⁸¹⁹

Read the table as two tools for two jobs. A scan gives a detailed picture on one day. A scale gives a cheap reading every day, which is only worth having if you accept that the number is an estimate.

Can you get a DEXA scan on the NHS?

Yes, but for bones, not for body fat. The NHS says a scan may be needed if you are over 50 with a risk of osteoporosis, or younger with other risk factors such as smoking or an earlier fracture.¹ Its list of reasons also includes a fracture after a minor fall, arthritis, taking oral steroid tablets for 3 months or more, and an early menopause.²

NICE’s osteoporosis guideline NG259, published on 29 July 2026, recommends offering a DEXA scan to measure bone density to people aged 30 and over after certain fragility fractures. It also suggests considering a scan to guide treatment when the 10-year risk of a major osteoporotic fracture is 10% or more.⁴

For whole-body scans, the NHS is plain. It says they can also measure bone, fat and muscle, but in adults they are used only as part of a research study.² The NHS lists DEXA among the types of X-ray as a test of bone density, and does not mention body composition there.¹⁷

One caution on dates. The three NHS DEXA pages read were last reviewed on 5 October 2022, and their next review date of 5 October 2025 has passed.¹²³ They are still the NHS’s published position, but check nhs.uk for any newer wording.

The NHS bone scan is also not the same test as a private body scan. It usually covers the hip and lower spine and takes 10 to 20 minutes.³ Results are given as a T-score, which compares your bones with those of a healthy young adult. A T-score of −2.5 or lower is defined as osteoporosis.³ A T-score is a bone measure. It does not give a body fat percentage.

How much does a private DEXA scan cost in the UK?

Prices vary by centre, and most operators do not publish a single tariff. The figures below were read on 20 October 2026 and are all “from” prices. Treat them as a starting point and check the centre’s own quote.

A worked example: scanning twice a year

Suppose someone books 2 scans a year for 3 years, which is 6 scans. This is arithmetic only, not a recommended schedule. At £125 a scan the total is 6 × £125 = £750. At £180 it is 6 × £180 = £1,080. At the Nuffield bone scan guide price of £230 it is 6 × £230 = £1,380, although that is a bone scan, not a body composition one.

A single scan is a smaller outlay than those totals suggest, and it may be all you want. The point of the sum is only to show how the cost grows if scans are repeated, and the research below gives a reason not to repeat them without need.

How accurate is each method, and how wrong can a smart scale be?

No study read compares a Chutex scale with DEXA. What exists is research on other devices. It points the same way: bioimpedance tracks DEXA loosely, with errors that matter for a single reading.

• French smart scales. In a study that compared three smart scales with DEXA in patients, the median error in body weight on the first scale was 0.3 kg (0.66 lb). For fat mass the median errors were −2.2 kg, −4.4 kg and −3.7 kg (4.85 lb, 9.70 lb and 8.16 lb) on the three scales, with wide interquartile ranges. A minus sign means the scale gave less fat than DEXA. The authors concluded that smart scales are not accurate for body composition and should not replace DEXA in care.⁷ Only the abstract was read.
• A professional multi-frequency device. In 1,000 healthy adults, a professional device (not a home scale) gave body fat percentages 4.2 points lower than DEXA in men and 2.8 points lower in women, with a spread (standard deviation) of ±3.0 and ±2.6 points. Repeat readings agreed closely with each other. Visceral fat was the weakest match to DEXA.⁸
• Athletes. A systematic review and meta-analysis of BIA against DEXA in athletes (5 studies in the pooled result) found that BIA overestimated fat-free mass by 2.78 kg (6.13 lb), with a 95% confidence interval of 1.38 to 4.18 kg.⁹
• The equations behind BIA. A large reference study of 1,829 people reported root mean square errors of 3.9 kg for men and 2.9 kg for women on fat-free mass.¹⁹

To put one of those errors in everyday units: 4.4 kg is 9.70 lb, or nearly 0.7 of a stone. A reading that far out in fat mass tells you little on its own. A change from one week to the next is more useful, as long as conditions stay the same.

The BIA method also depends on assumptions. It treats lean mass as holding almost all of the body’s water, with a constant level of hydration, and results vary with the equation used, the sample, age and ethnic origin.¹⁸ The British Heart Foundation says a scale can overestimate fat if you are dehydrated, and advises weighing at the same time of day in similar conditions.¹⁰

For a closer look at how scales perform in independent tests, see how accurate smart scales are.

Radiation, safety and who should skip a scan

The NHS says bone density scans are very safe, with a radiation level well below that of standard X-rays.¹ It does not recommend them in pregnancy, because X-rays can harm an unborn child, and says the radiographer may stay in the room during the scan because the dose is low.¹ The 2020 review also names pregnancy as the only relative contraindication to a whole-body scan.⁶

How big is the dose?

The review puts a whole-body scan with a recent scanner at about 4 to 5 µSv, and says the dose depends on the settings, the size of the person, the number of images and the scan time.⁶ That figure comes from this review, not from the UK Health Security Agency (UKHSA) or the NHS. No DEXA line was found on the UKHSA dose comparison page read.⁵

For scale, UKHSA says people in the UK are exposed to about 2.6 mSv a year from natural and other sources, and gives 0.014 mSv for a chest X-ray.⁵ In the same units, 2.6 mSv a year is about 7.1 µSv a day (2,600 ÷ 365). So 4 to 5 µSv is about 0.56 to 0.70 of an average day’s radiation, and roughly 0.29 to 0.36 of a chest X-ray at 14 µSv. These are comparisons, not a verdict that any dose is risk-free.

Scan.com says DEXA does involve ionising radiation, though the risk is extremely low, and advises against it in pregnancy unless there is a clear net benefit.¹⁵ People with a pacemaker or other implanted electronic device should not use a body fat scale.¹⁰¹¹

How often is a scan or a scale reading useful?

For bones, NICE suggests re-assessing with a DEXA scan within 2 to 3 years if a person was close to the treatment threshold, or at 5 years if nothing has changed clinically.⁴ That is a bone question, not a body composition one.

For body composition in healthy people, the athlete meta-analysis says medical justification should always exist for DEXA and that it is not recommended for repeated longitudinal measurements in healthy subjects.⁹ Nuffield Health says that for athletes, body composition scans are typically used twice a year.¹⁶ No UK institutional source read gives a recommended interval for body composition scans, so this page does not give one.

A scale is different, because it uses no radiation. The advice that has a source is to weigh yourself at the same time of day and in similar conditions, after drinking enough.¹⁰

How to use both: a scan as a benchmark, a scale for the trend

If you do have a private scan, a scale can still be useful afterwards. The aim is to use the scan as a one-day reference, and the scale to follow the direction of travel. This is a practical method, not one validated by any source read, and it promises no particular accuracy.

1. Have the scan after an overnight fast if the centre allows it, because meals shift lean mass readings.⁶
2. On the same morning, weigh on your scale in the way you will use it every day, after drinking normally.¹⁰
3. Write down the difference between the scale’s body fat figure and the scan’s. That gap is your scale’s offset on that day.
4. From then on, read the scale at the same time and in the same conditions, and watch how the figure moves over weeks.
5. Do not assume the gap stays fixed: in the French study, the error in fat mass was linked to weight, BMI and body composition, depending on the scale, so the gap can move as your body changes.⁷

Seen this way, the two are not rivals. A scan is a detailed picture taken now, and a scale is an inexpensive way to see whether things are moving. For other measures worth tracking alongside, see waist measurement and visceral fat.

Frequently asked questions