Ahrefs vs SimilarWeb: Which Traffic Tool Is Actually Accurate? [2026 Data]

Do not index

If you've ever looked up the same website in Ahrefs and SimilarWeb and got completely different numbers, you're not imagining things. The gap between the two tools is real — and for startup-scale sites, it can be 3x to 10x.

This post explains why that happens, what independent accuracy research shows about both tools, and which one is actually worth trusting for different use cases.

Quick answer: Ahrefs only measures organic search traffic and consistently underestimates total visits. SimilarWeb estimates all traffic channels but its accuracy degrades sharply for sites under ~100,000 monthly visits. For early-stage startups, both tools produce unreliable numbers — which is the core reason verified traffic data exists as a category at all.

Why Ahrefs and SimilarWeb Show Different Numbers for the Same Site

The reason the two tools disagree is that they're measuring completely different things — not different versions of the same thing.

Ahrefs calculates organic search traffic only. It crawls the web, builds a keyword index, identifies which pages rank for which terms, and then estimates traffic by multiplying: ranking position × estimated search volume × expected CTR for that position. If a site gets visitors from newsletters, social, direct word-of-mouth, paid ads, or referrals, Ahrefs sees none of it.

SimilarWeb estimates all traffic channels. It pulls data from browser extensions installed on millions of users' computers, ISP-level data partnerships, third-party clickstream panels, and machine learning models that extrapolate from all of the above. It then estimates direct visits, organic visits, referral traffic, social traffic, email, and paid — combined into a total monthly visits figure.

A startup getting 20,000 monthly visitors mostly from a viral launch, a newsletter, or direct brand traffic could show as near-zero in Ahrefs and 12,000–40,000 in SimilarWeb. Neither number is the real one.

A startup built primarily on SEO might show closer figures in both tools — but even then, methodology differences mean they won't match exactly.

What Independent Accuracy Research Actually Shows

The best publicly available accuracy study on third-party traffic tools was published by Rand Fishkin at SparkToro using 641 sites and 7,692 months of data. It compared estimated traffic from multiple tools against actual Google Analytics figures.

Key correlation scores (where 1.0 = perfect accuracy):

Tool	Correlation with actual GA data
SEMrush	0.790
SimilarWeb	0.659
Ahrefs	0.504*

\Ahrefs measures organic traffic only. When correlated against Google Search Console organic data specifically — a fairer comparison — their accuracy came out at ~0.75.*

A separate 2024 study by Collaborator.pro measured average error rates across 184 websites:

Tool	Average error rate	Bias
Ahrefs	48.6%	Underestimates
SimilarWeb	57.0%	Overestimates
SEMrush	61.6%	Overestimates

To translate that into plain terms: on average, the number a tool shows you for any given site is off by roughly half. For some sites the error is minor. For smaller sites — particularly those under 50,000 monthly visits — the error bars widen to +/- 100% or more, meaning a tool might report 50,000 visits when a site actually received 5,000 or 100,000.

That's not a flaw in these tools. It reflects a fundamental constraint: website traffic is private by default, and any tool working from external signals will have variance. The question is when that variance matters for your decision.

SimilarWeb: Strong at Scale, Unreliable for Early-Stage Sites

SimilarWeb is the most widely used traffic intelligence tool on the market. For large, established websites — major e-commerce brands, media publishers, SaaS companies with hundreds of thousands of monthly visitors — its estimates are often directionally accurate.

The SparkToro research shows SimilarWeb is strongest in the middle of the traffic range (roughly 5,000–100,000 GA users/month). For very large sites, even SimilarWeb's error bars widen considerably.

For early-stage startups under 50,000 monthly visits, SimilarWeb often has too few real panel observations to extrapolate reliably. The result: estimates that can overshoot or undershoot by 3–5x, or "no data available" for sites it hasn't seen enough of.

SimilarWeb is the right tool when:

You're researching a large, established competitor (above ~100k monthly visits)

You need a channel breakdown — what proportion of traffic is organic vs paid vs referral

You're doing top-level market sizing or share-of-voice analysis

SimilarWeb is less reliable when:

The site you're researching has under 100,000 monthly visits

You need accurate total traffic for early-stage startup benchmarking

You're using estimates to make specific growth decisions

Pricing: Limited free tier. Paid plans start in the hundreds per month. Enterprise plans significantly more.

Ahrefs: Accurate for Organic, Blind to Everything Else

Ahrefs started as a backlink tool and became the SEO industry standard. Its traffic estimates are based entirely on organic search: keyword rankings multiplied by search volume and CTR curves.

This makes Ahrefs highly accurate for one specific question: how much traffic is a site getting from Google? For that use case, at sites with stable rankings, Ahrefs performs well. The Collaborator research ranked it first for accuracy among the three tools tested, with an average error rate of ~49%.

But Ahrefs has a hard blind spot: it sees nothing outside of organic search. A startup whose growth comes primarily from word-of-mouth, an email list, a Product Hunt launch, or paid acquisition will look essentially invisible in Ahrefs — regardless of actual traffic.

Ahrefs is the right tool when:

You're doing SEO competitive research (keywords, backlinks, content gaps)

You want to understand a competitor's organic search footprint

You're auditing your own organic performance

The site you're researching is primarily SEO-driven

Ahrefs is less reliable when:

You want total traffic (it only shows the organic slice)

The site you're researching doesn't grow primarily through search

You're benchmarking early-stage startups whose channel mix is unknown

Pricing: Starter plan from ~$29/month. Full-featured plans from $99–$999+/month.

A Brief Note on SEMrush

SEMrush occupies similar territory to both tools: organic keyword data (like Ahrefs) plus broader competitive traffic estimates (like SimilarWeb). The SparkToro research gave it the highest correlation score against real GA data (0.790), though it tends to overestimate — the Collaborator research found a 61.6% average error rate with a systematic overestimation bias.

For most startup use cases, SEMrush and Ahrefs are roughly interchangeable for keyword and SEO research. SimilarWeb remains the better option for channel-level traffic intelligence on larger sites.

The Side-by-Side

	SimilarWeb	Ahrefs	SEMrush
What it measures	All channels (estimated)	Organic search only (estimated)	Organic + some broader estimates
Best accuracy range	Sites above ~100k monthly visits	Sites with stable SEO rankings	Mid-to-large sites
Average error rate	~57%	~49%	~62%
Bias	Overestimates	Underestimates	Overestimates
Useful for channel mix?	Yes	No	Partially
Useful for startup benchmarking?	Unreliable under 50k visits	Organic only	Unreliable under 50k visits
Pricing	Free tier / $$$ enterprise	$29–$999+/month	$99–$499+/month

The Startup Accuracy Problem — And Why Verified Data Is Different

Neither SimilarWeb nor Ahrefs was designed to answer the question most founders actually care about: is my traffic at this stage ahead, behind, or in line with comparable startups?

SimilarWeb's accuracy degrades at the exact scale most early-stage startups operate at. Ahrefs only measures the organic channel, which is often a minority of early-stage traffic. Both tools are building estimates from external signals — they have no access to the actual analytics dashboards.

Verified startup traffic data is structurally different. When a founder connects their Google Analytics or Google Search Console to a platform like Trust Traffic, the data comes from the source — not from panel extrapolation or keyword modelling.

This matters in practice for two reasons:

Benchmarking becomes meaningful. If you can see verified monthly traffic from startups at seed stage — channel breakdown and growth trajectory confirmed against real analytics — you can answer "what does good look like at my stage?" with actual data. That question can't be answered reliably by SimilarWeb or Ahrefs.

The estimate problem disappears. "They have 50k visits and we only have 8k" could mean almost anything when both numbers are estimates. With verified data, the comparison is real.

See the Trust Traffic leaderboard →

Which Tool Should You Actually Use?

For competitive research on an established company (above ~100k monthly visits):

SimilarWeb is the right starting point for channel-level intelligence. Treat numbers as directional.

For SEO strategy — understanding keywords, content gaps, backlinks:

Ahrefs is the industry standard. It's the best tool for the organic search use case it was built for.

For benchmarking your own startup's traffic against peers at the same stage:

Neither SimilarWeb nor Ahrefs is reliable. Verified databases built specifically for early-stage startups give you the only real benchmark data.

For a quick sanity check on a large competitor:

Cross-reference SimilarWeb and Ahrefs. If they broadly agree, you can have more confidence in the direction. If they diverge significantly — common at smaller sites — discount both.

The Takeaway

The reason Ahrefs and SimilarWeb show different numbers is that they're not measuring the same thing. Ahrefs sees the organic slice; SimilarWeb estimates the whole picture from limited panel data. Neither is wrong — they're answering different questions with different methods and unavoidable error margins.

For most competitive research on mid-to-large companies, these tools are useful despite their limitations. For early-stage startup benchmarking, the estimates are too noisy to act on — which is why the category of verified, founder-connected traffic data exists at all.

If you're a founder trying to understand where your traffic stands against real peers, or an investor wanting benchmarks grounded in actual analytics rather than extrapolation, the Trust Traffic leaderboard is built for that use case.

Browse verified startup traffic data →

Sources: SparkToro traffic accuracy study, Collaborator.pro accuracy research