Moz calculates Page Authority (PA) using a machine-learning model that aggregates dozens of link-based signals from Moz’s Link Explorer web index into a single predictive score ranging from 1 to 100. The score is logarithmic — meaning it becomes progressively harder to improve as you climb higher — and it predicts how likely a specific page is to rank well in Google search results. Understanding how Moz calculates Page Authority helps SEOs benchmark page-level link equity, compare competitors, and prioritize link-building efforts.
Key Takeaways
- →Page Authority is scored on a logarithmic scale of 1–100 using Moz’s machine-learning model.
- →The primary inputs are the quantity and quality of external links pointing to a page.
- →PA is a relative metric — it shifts as the overall web index changes.
- →PA is correlated with ranking ability but is not a direct Google ranking factor.
- →Domain Authority (DA) measures the whole domain; PA measures a single page.
The Core Formula: What Goes Into the PA Score?
Moz does not publish a literal mathematical formula for Page Authority — instead, it trains a machine-learning algorithm against real Google search result data. The model is fed a wide array of link metrics collected from Moz’s own crawl index, and the output is a single score that best correlates with actual Google rankings.
The most heavily weighted inputs include:
- Linking Root Domains: The number of unique domains linking to the page. More authoritative unique domains = higher PA.
- Total External Links: Raw count of inbound links, though uniqueness is weighted more heavily than raw volume.
- MozRank: A link popularity score reflecting the quality and quantity of links pointing at a page, modeled on a flow-of-authority concept similar to PageRank.
- MozTrust: Measures how close a page is to trusted seed sites (e.g., government and education domains), rewarding pages that earn links from trustworthy sources.
- Link Profile Quality: The PA of the pages that link to the target page — a link from a PA 80 page contributes far more than one from a PA 15 page.
All of these signals are combined through the ML model to produce the final 1–100 score. Moz periodically retrains the model against fresh Google SERP data, which is why PA scores can fluctuate even when no changes have been made to a page.
How Moz Calculates Page Authority: The Logarithmic Scale Explained
The 1–100 range is logarithmic, not linear. This is one of the most important practical details about how Moz calculates Page Authority. On a linear scale, moving from 10 to 20 would require the same effort as moving from 50 to 60. On a logarithmic scale, moving from 50 to 60 requires exponentially more link equity than moving from 10 to 20.
In practice, this means:
- A brand-new page with zero links starts at PA 1.
- Earning a handful of quality links can quickly push a page to PA 20–30.
- Reaching PA 50+ requires a substantial, high-quality inbound link profile.
- Pages above PA 70 are typically major publications, Wikipedia articles, or heavily linked cornerstone content.
Because of this logarithmic compression, absolute PA numbers matter less than relative comparisons. A page with PA 45 competing against PA 40 pages is well-positioned; the same PA 45 page competing against PA 65 pages faces a steep uphill battle.
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Page Authority is best used as a comparative tool — not an absolute grade. Two points of PA difference at the top of the scale can represent millions of links of difference in the underlying data.
— Moz, Page Authority Documentation
PA vs. DA: Understanding the Difference
Moz produces two closely related authority metrics. Knowing when to use each is critical for accurate SEO analysis.
| Metric | Page Authority (PA) | Domain Authority (DA) |
|---|---|---|
| Scope | Single URL / page | Entire root domain |
| Primary Use | Evaluate individual page strength | Evaluate overall site authority |
| Best For | Competitor page-level benchmarking | Prospecting link-building targets |
| Scale | 1–100 (logarithmic) | 1–100 (logarithmic) |
| Calculated By | ML model on page-level link data | ML model on domain-level link data |
| Google Ranking Factor? | No — a Moz proxy metric | No — a Moz proxy metric |
Why PA Scores Fluctuate (Even Without Doing Anything)
One of the most common points of confusion is that a page’s PA can drop even when no links have been lost and no on-page changes have been made. This happens for two key reasons:
PA is calculated relative to every other page in Moz’s index. If the web grows and millions of new high-authority pages are added, your PA can decrease even though your own link profile hasn’t changed.
Moz periodically retrains its ML model against fresh Google SERP data. When the model is updated to better reflect current Google behavior, all PA scores are recalibrated simultaneously.
This is why Moz explicitly advises tracking PA trends over time and comparing pages within the same competitive set, rather than treating any single PA number as an immutable grade.
How to Improve Your Page Authority Score
Because PA is driven almost entirely by link-based signals, the strategies to improve it are rooted in link acquisition and link equity optimization:
A single link from a PA 70+ page can move your score more than 50 links from PA 20 pages. Prioritize editorial placements on authoritative publications in your niche.
Internal links pass link equity from your high-PA pages to pages you want to boost. A well-structured internal linking strategy can meaningfully improve PA for deep content pages.
Spammy or low-quality inbound links can dilute your link profile’s overall trust signals. Audit and disavow harmful links to ensure your PA reflects only legitimate authority.
Original research, comprehensive guides, free tools, and data-driven content naturally attract backlinks at scale. The more a page is cited, the faster its PA grows.
If you have duplicate or near-duplicate pages splitting link equity, consolidate them with 301 redirects. This concentrates authority into a single canonical URL, boosting its PA.
Frequently Asked Questions
The Bottom Line
Understanding how Moz calculates Page Authority gives you a significant edge in competitive SEO analysis. PA is a machine-learning score built from dozens of link-based signals — primarily the quantity, quality, and trustworthiness of inbound links — compressed into a logarithmic 1–100 scale that predicts ranking potential. It is a relative metric that shifts with the broader web, so the smartest way to use it is as a competitive benchmarking tool rather than a fixed target. Focus on earning authoritative backlinks, building smart internal linking structures, and creating content worth citing — and your Page Authority will follow.
