Pulse oximeters: what the number means — and what it doesn't
A small clip on your fingertip can estimate your blood oxygen in seconds. We explain normal ranges, the accuracy limits worth knowing about, and how to read a result honestly — without the hype.
A pulse oximeter estimates your blood oxygen saturation (SpO2) as a percentage, alongside your pulse rate.
- 95–100% — generally considered normal for a healthy adult at rest.
- 93–94% — lower than usual; worth watching, and worth a call to NHS 111 or your GP if it's a change for you or you feel unwell.
- 92% or below — NHS guidance is to seek urgent help (ring 999 or attend A&E), unless you've been told a different target by a clinician.
People with long-term lung conditions (such as COPD) may have a personal target range set by their team that is lower than 95% — always follow the figure your clinician gives you, not a generic chart.
Types of pulse oximeter compared
Most home users only ever need a basic fingertip clip. Here's how the main categories stack up.
| Type | Best for | Watch for | Typical cost |
|---|---|---|---|
| Fingertip clip | Spot-checks at home for adults | Won't fit small children's fingers well; battery-only | £15–£40 |
| Handheld with probe | Frequent monitoring, carers, larger fingers | Bulkier; pricier; probe care | £40–£120 |
| Paediatric / infant | Children and babies (with clinical advice) | Get the right size; readings need clinical context | £25–£60 |
| Smartwatch / wearable SpO2 | Casual trend-spotting, not diagnosis | Wellness-grade, not a medical device; least accurate | Bundled in watch |
Indicative categories and typical UK prices — for orientation only, not a product recommendation.
What to look for
If you're buying a fingertip oximeter for home use, these are the things that genuinely matter.
A 'CE' or 'UKCA' mark and MHRA-registered medical device status
Buy one sold as a medical device, not a 'wellness gadget'. The MHRA expects a stated accuracy (root-mean-square error) under 4% across the normal range.
A clearly stated accuracy figure
Reputable models declare roughly ±2% over 70–100% SpO2. If the listing won't tell you the accuracy, treat that as a red flag.
A clear, well-lit display
You want both SpO2 and pulse shown plainly, ideally with a signal/perfusion indicator so you know the reading is steady before you trust it.
The right size for the user
A standard adult clip won't read reliably on a small child's finger. For children, choose a paediatric device and take advice from your GP or pharmacist.
Honest labelling about limitations
Better brands now acknowledge that skin tone, cold hands and poor circulation can affect readings. That candour is a good sign.
How to take an accurate reading
Technique matters as much as the device. A poor reading usually means poor conditions, not a faulty unit.
Warm your hand first
Cold fingers and poor circulation (including Raynaud's) are the commonest reason for a weak or failed reading. Rest your warmed hand on your chest for a few minutes before measuring.
Remove nail varnish and false nails
Dark shades — blue, green, black, purple and brown — interfere most and can pull the reading down by several percent. Bare nails give the clearest light path.
Sit still and let it settle
Movement scrambles the signal. Stay still for 30–60 seconds and use the reading once the number and the pulse trace have steadied.
Read it in context
One low reading on a cold morning isn't the same as a sustained drop. Note how you feel and whether it's a change for you, then act on the trend — not a single blip.
A reliable, inexpensive fingertip pulse oximeter is a genuinely useful home tool for keeping an eye on a known condition — provided you understand its limits. It is a guide, not a diagnosis. Crucially, UK and international research shows oximeters can over-read by roughly 0.6–1.5 percentage points in people with darker skin tones, meaning a 'reassuring' number can occasionally mask a genuinely low oxygen level. Never let the gadget overrule how you actually feel.
Adults monitoring a known lung or heart condition at home, on advice from their clinician.
Over-reading in darker skin tones, cold hands, nail varnish and movement. If you feel breathless or unwell, seek help regardless of the number.
Pulse oximeters: your questions answered
What is a normal blood oxygen reading?
For most healthy adults at rest, 95–100% is normal. Some people with chronic lung conditions have a lower personal target set by their clinician — follow that figure if you've been given one. NHS guidance is to seek urgent help if your reading is 92% or below.
Are pulse oximeters less accurate on darker skin?
Yes — this is the single most important limitation to understand. Studies of devices used in the NHS COVID Oximetry @home scheme found readings 0.6–1.5 percentage points higher for people with darker skin tones at the same true oxygen level, which can cause genuinely low readings to be missed. The MHRA has called for further review. Treat your symptoms, not just the number, and tell a clinician if you feel worse even with a 'normal' reading.
Does nail polish really affect the reading?
It can. Dark shades in particular — blue, green, black, purple and brown — can cause underestimation of several percent. Remove varnish and false nails from the finger you're testing for the clearest result.
Why won't my oximeter give a reading?
Usually cold hands, poor circulation or movement. Warm your hand, rest it still on your chest for a few minutes, then try again. If a warm, still finger still won't register, the device or its batteries may be at fault.
Can a smartwatch replace a proper pulse oximeter?
Not for clinical decisions. Most wearable SpO2 features are sold as wellness tools, not registered medical devices, and tend to be the least accurate. For monitoring a health condition, use a CE/UKCA-marked oximeter and follow your clinician's advice.
Is this medical advice?
No. This guide is educational. For anything about your own health — symptoms, a worrying reading, or which device suits you — speak to your GP, NHS 111, or a pharmacist.
One number is never the whole story
A pulse oximeter is a helpful signpost, not a verdict on your health. If you feel breathless or unwell, contact NHS 111, your GP, or call 999 — whatever the screen says. Explore our other plain-English monitoring guides to choose home health tools with confidence.