How TrustWatt ratings work

TrustWatt helps drivers and partners make better decisions using real-world reviews. We use two main measures:

Average Rating (out of 5): a simple view of the average customer rating
TrustWatt Index (out of 100): a confidence score that considers quality, volume and trust signals

This page explains how both work.

1. Our 10-point rating scale

When a driver leaves a review on TrustWatt, we collect ratings on a 1–10 scale.

Why 1–10? It gives a bit more detail than 1–5, while still feeling simple.

Depending on what's being reviewed, drivers can rate things like:

EVs: range, comfort, tech, practicality, running costs, reliability and more
Chargers: reliability, ease of use, smart features and value
Installers: communication, punctuality, workmanship, tidiness and value

2. How we show Zap ratings (out of 5)

Although we store ratings on a 10-point scale, we display the overall rating as Zaps out of 5 because it aligns with our brand and keeps things simple.

Conversion rule

We convert 1–10 into 0.5–5 Zaps and round to the nearest half-Zap.

Examples:

10/10 → 5.0 Zaps
9/10 → 4.5 Zaps
8/10 → 4.0 Zaps
7/10 → 3.5 Zaps
6/10 → 3.0 Zaps

3. What TrustWatt Index is (and what it isn't)

TrustWatt Index is a 0–100 confidence score used on TrustCentre pages.

It is not just "star rating × 20".

TrustWatt Index is designed to answer a different question:

"How confident should I be in this rating, based on how much evidence and trust signals exist?"

4. How TrustWatt Index is calculated

TrustWatt Index combines four signals:

A) Rating quality (50%)

This reflects how strong the average rating is. Higher average rating = higher TrustWatt Index contribution.

B) Review volume (20%)

More reviews generally means a more reliable picture. Going from 2 reviews to 20 matters more than going from 200 to 220. That's why we use a curve (not a straight line).

C) Verification (15%)

The more we know about who left a review, the more it counts. Every published review sits on one of three rungs of our verification ladder:

Verified email — the reviewer confirmed their review by clicking a link sent to their email address. Counts at 65%.
Verified account — the reviewer holds a TrustWatt account with a confirmed email address. Counts at 90%.
Verified owner — we hold evidence, such as a photo, invoice or installation record, that the reviewer really bought or had installed what they are reviewing. Counts in full.

Reviews that reach us through a trusted route, such as a verified installation or an invitation from a partner, start higher up the ladder. Nothing is published until at least the email step is complete.

D) Recency or baseline (15%)

We want TrustWatt Index to reflect whether the evidence is current, but we also don't want to penalise new profiles unfairly. So we use a recency factor once there's a meaningful number of reviews, or a baseline for newer profiles while they build up evidence.

5. What "confidence" means on TrustWatt

You may see a confidence label such as:

New: no reviews yet
Building confidence: early evidence (small number of reviews)
High confidence: enough reviews and signals for a stable picture

This helps explain why two profiles with similar Zap ratings can have different TrustWatt Index scores.

6. What happens when there are no reviews yet?

If a company or product has 0 reviews, we do not show a "0" TrustWatt Index. Instead, we show a neutral "New" state until reviews are submitted.

7. Zap distribution charts

Sometimes we show charts like "5-Zap, 4-Zap, 3-Zap" breakdowns. These charts are based on the same Zap conversion logic used across the site, so what you see in the distribution matches what people see in the Zap rating.

7b. Reference records and how they affect scores

To build and test the platform before we had a reviewer community, we created a set of reference records covering vehicles, chargers and installers. These were built by us, they are not customer reviews, and they are labelled as reference data wherever they appear.

Reference records are retired item by item. Once a vehicle, charger or installer has enough genuine reviews to stand on its own, its reference records drop out of the public score and out of public display. Full detail is in our Reviews Policy.

8. Removing fake or misleading reviews

TrustWatt takes review integrity seriously. We may remove or moderate reviews that:

are clearly fake or spam
contain hate speech or illegal content
include personal data that shouldn't be shared
are clearly not about the product or service being reviewed

If you believe a review is inaccurate or breaches our guidelines, you can report it from the review page.

9. Questions

If you have questions about how ratings or TrustWatt Index works, contact TrustWatt Support.