MarketSizer & Apollo
Apollo brings the contact database and the sequences. MarketSizer tells you which accounts are worth them this week. Teams that shortlist the two usually stop choosing and wire them together.
“The end-to-end AI sales platform.”
Source: apollo.io homepage
What each tool does well
Apollo
Best known for
A large B2B contact database bundled with email, phone and LinkedIn sequencing in a single self-serve seat.
Useful for
SDR and AE teams running high-volume outbound who want contact data and outreach automation in one platform.
MarketSizer
Best known for
Subscription intelligence - accounts ranked by observable buying events like trials, switches, churns and renewals.
Useful for
GTM teams that already have contact data and want an intelligence layer to time outreach around vendor changes across 140+ countries.
Where Apollo is strong
- One of the largest self-serve B2B contact databases available to individual reps.
- Native email, phone and LinkedIn sequencing means data and sending live in the same seat.
- Popular free plan gives new teams a zero-friction way to get started.
- Broad Chrome-extension coverage for lookups on LinkedIn and any company site.
- Deep integration ecosystem across the major CRMs (HubSpot, Salesforce, and others).
- Firmographic and hiring-signal filters that are useful once you know which segment to work.
Where they differ
Different jobs on the same pipeline - the overlap between Apollo and MarketSizer is smaller than a feature list suggests.
| Feature | Apollo | MarketSizer |
|---|---|---|
| Data coverage | ||
| B2B contact database (email, phone, LinkedIn) | Included | Email, phone and LinkedIn via built-in enrichment |
| Firmographic filters (employee count, revenue, geo) | Included | Included |
| Technographic snapshot (what a site runs today) | Included | Included |
| Historical subscription record per account | Not included | Included |
| Global country coverage | Included | Included |
| Buying signals | ||
| Topic and website-visitor intent | Bombora topic intent + visitor intent | Subscription events |
| Hiring and funding-round filters | Included | Hiring and funding context via enrichment |
| Category-level competitor trial detection | Not included | Included |
| Vendor switch and churn events | Not included | Included |
| Renewal-window timing | Not included | Included |
| Signal explainability at the event level | Rolled-up intent score | Included |
| Workflow and activation | ||
| Native email sequencing | Included | Push to Instantly, Brevo or your CRM |
| Native dialer and meeting scheduler | Included | Not included |
| Two-way CRM sync | Included | HubSpot, Pipedrive and Zoho CRM |
| Chrome-extension side panel | Included | Included |
| Bulk list enrichment | Included | Included |
| Pricing model | ||
| Free tier | Included | Free trial |
| Pricing basis | Seat-based | Usage credits |
MarketSizer pricing as published at marketsizer.io/pricing. Apollo details as published on their own site and public documentation, last checked 8 August 2026. Spotted something out of date? Tell us and we will fix it.
Where each tool earns its place
Lean on Apollo when
- Your primary need is contact lookup and email sequencing in a single self-serve seat.
- High-volume outbound is your motion and contact volume is the bottleneck.
- Bombora topic intent plus visitor intent covers your signal needs at the account level.
- You want a free plan so a whole team can start without procurement.
- You value a native dialer and meeting scheduler alongside email sequencing.
Add MarketSizer when
- You want to prioritise accounts by observable buying events, not filter a static list.
- Timing matters as much as targeting - you would rather work 50 in-market accounts than 500 cold ones.
- You already have a contact-data source and want an intelligence layer on top of it.
- You want to know when an account is about to change vendors, rather than only what they use today.
- You want accounts ranked by ICP fit, purchase intent and win likelihood in one Opportunity Score, with the evidence attached.
How MarketSizer works with Apollo
Apollo answers who to contact and how to reach them at scale. MarketSizer answers which accounts are worth reaching this week, and why. Wired together, Apollo sequences fire at accounts with a live buying event behind them instead of working a static list top to bottom.
MarketSizer flags in-market accounts
Subscription events - a competitor trial, a vendor switch, an approaching renewal - rank the accounts worth working now, each with the evidence attached.
Hand them to Apollo
Export flagged accounts as a CSV that Apollo imports into a list or sequence, or sync them through a shared CRM such as HubSpot that Apollo reads from.
Reps keep the signal in view
The MarketSizer Chrome extension opens as a side panel while reps work in Apollo, so the event behind each account sits next to Apollo’s contact data.
Outreach fires on timing, not volume
Sequences go out to accounts with a live buying event behind them, and the signal gives reps a first line that reads as relevance rather than luck.
What buyers say about the category
Themes from GTM leaders currently evaluating tools in this space.
Coverage fit comes up first: the database is vast, and how well it maps to a specific niche varies by segment. The switching question comes up second. Apollo's intent tells you which topics an account is researching; it stays quiet on whether they are actively trialling or leaving a competitor. Neither theme makes Apollo the wrong choice. They make it a different tool for a different job.
“Knowing an account runs Salesforce is where the useful questions start, not where they end. Which parts do they actually use, and what are they about to change?”
“We stitched together our own signals across a couple of tools. Building them took longer than expected, keeping them accurate takes even longer, and we still second-guess the output.”
MarketSizer & Apollo - frequently asked questions
Is MarketSizer a replacement for Apollo?
For most teams, no - the two sit alongside each other. MarketSizer surfaces accounts by buying-event signals (trials, switches, churns, renewals). Apollo supplies contact data and outbound sending. Teams typically use MarketSizer to decide which accounts to work and Apollo (or a similar tool) to reach the people inside them.
Does the MarketSizer Chrome extension work inside Apollo?
Yes. SignalOps - the MarketSizer Chrome extension - opens as a side panel while you work in Apollo, so when you are building a list or reviewing a company in Apollo you see MarketSizer signals beside Apollo’s data.
Can MarketSizer push accounts into Apollo?
Yes, via a short handoff rather than a native connection. Accounts flagged by MarketSizer signals export as a CSV that Apollo imports into a list or sequence, or sync through a shared CRM (HubSpot, Pipedrive or Zoho CRM) that Apollo reads from.
How is MarketSizer different from Apollo intent data?
Apollo intent combines Bombora topic-level buying intent (15,000+ topics, per Apollo's knowledge base) with website-visitor intent. MarketSizer signals are event-based - a trial started, a vendor switched, a subscription approaching renewal - and each signal is attached to the underlying account event, not to a cookie or a rolled-up score.
Does MarketSizer include contact data like Apollo?
Yes. MarketSizer includes contact data - email, phone and LinkedIn details for the people inside a target account, enriched on demand alongside the company-level signals. The proprietary layer underneath is the subscription-event and buying-signal dataset rather than a static contact database, so most teams pair MarketSizer with Apollo or a similar tool as their primary contact source.
How do teams typically use MarketSizer and Apollo together?
Most teams use MarketSizer to identify in-market accounts based on company-level buying signals, then hand those accounts to Apollo via CSV export or a shared CRM. Apollo handles sequencing and outreach, while MarketSizer provides the account context reps use to personalise messaging. Reps can also view MarketSizer insights in the Chrome extension side panel on supported pages, including when working in Apollo.
What does MarketSizer cost compared with Apollo?
Apollo is seat-based; MarketSizer is credit-based (see current plans). There is no per-seat multiplier - the whole team can use it. Apollo’s free plan is one of the strongest in SaaS and remains a good reason to keep it in the stack alongside MarketSizer.
When would a team move off Apollo entirely?
Rarely - Apollo is primarily outreach automation and MarketSizer is primarily intelligence. The exception is a team using Apollo only for prospecting and not for sequencing, where MarketSizer plus a lighter outreach tool (Instantly, Brevo) can replace the workflow at a lower blended cost.
See how MarketSizer works with your Apollo stack.
30 minutes on your accounts, tailored to your ICP. We show which companies are trialling, switching or renewing right now, so you can see whether the timing signal changes what your team does next.
500 credit trial No credit card Live data, not a slide deck
Apollo and all other product names, logos and brands referenced on this page are trademarks of their respective owners, used for identification and comparison purposes only. No endorsement or affiliation is implied.