Every "best of" guide on this site carries a score out of 10. This page explains exactly how those scores are produced, what each number rests on, and where the gaps are. If a figure on this site is not something we measured ourselves, it says so.
The five criteria
| Criterion | Weight | What it measures |
|---|---|---|
| Noise | 25% | dB(A) at 1 m in the same reference room, with the ambient floor stated. A diffuser that runs all night is judged mainly on this. |
| Runtime | 20% | Hours of continuous and intermittent operation from a full tank, at a comparable mist level. |
| Coverage efficiency | 15% | Rated coverage per 100 ml of tank. This keeps a 500 ml unit from beating a 180 ml one simply by being bigger. |
| Build and materials | 20% | What the housing, cover and reservoir are made of, how the unit is finished, and how it holds up to daily handling. This is the one editorial component, and it is capped at 20% so opinion cannot decide a ranking on its own. |
| Customer rating | 20% | Verified customer reviews — but only counted when a product has 20 reviews or more. Below that the rating is shown with its review count and left out of the score. |
The reference room
All noise and runtime comparisons are made against a single reference space: a closed room of 30 m² (320 sq ft) with no forced airflow. Scent behaves completely differently in an open-plan floor than in a bedroom, so comparing two diffusers tested in different spaces tells you nothing. Where a product is rated for a smaller or larger space than the reference, we say so rather than adjusting the number.
Where each number comes from
Every figure in a comparison table carries one of three labels:
- Independent laboratory measurement — the figure comes from testing carried out by an independent test laboratory, not from our own marketing copy. Every Scentreat noise and runtime figure on this site sits in this tier.
- Manufacturer specification — published by whoever makes the product. Accurate as published, not independently verified. Competing products sit in this tier.
- Retailer listing — taken from the product page where it is sold. The weakest tier, and the one most likely to drift.
The distinction matters most for noise. A "30 dB" figure with nothing behind it is not a measurement; it is a marketing number. The Scentreat range has been noise- and runtime-tested by an independent laboratory, and those are the figures we publish. Where a number comes from someone else's spec sheet instead, we say so.
When a figure is missing
Most diffuser brands do not publish a decibel figure at all. On 10 September 2026 we checked the product pages of AromaTech, ASAKUKI, InnoGear, Saje, URPOWER, Pura, Aera and Saint Charles: none of them states a dB number, and several describe the product only as "whisper quiet". Vitruvi is the exception — it puts the Stone Diffuser at around 30 decibels on its own product page.
Where a brand publishes nothing, the comparison table says Not published. It does not say "about 30 dB", and it does not carry a number we guessed from the category. A product with no published figure simply scores nothing on the noise criterion, and the remaining four criteria are re-weighted across it — so a missing figure costs a product ranking positions rather than silently earning it an average one.
Where the gaps are
We have not bought and bench-tested competitor products. Where a competing diffuser appears in a comparison, its noise and runtime figures are taken from that brand's own published specification or from its retailer listing, and are labelled accordingly. That means a Scentreat figure and a competitor figure in the same row are not always established the same way — the label tells you which is which, and we would rather show that than quietly present them as equivalent.
Two things we do not publish, because we do not have them: a lead and cadmium migration test on the ceramic (EN 1388), and an ETL listing. The certifications the range does hold are CE and RoHS.
Disclosure
Scentreat sells diffusers. Any Scentreat product in a comparison table is marked as our own. We think a scoring system is only worth reading if you can see where the products we sell lose as well as where they win, which is why the score breakdown is published rather than just the total.
Corrections and dates
Prices and specifications change. Each comparison table carries the date it was last checked. If you find a figure on this site that does not match what the manufacturer publishes, write to support@scentreat.com and we will correct it and note the change.