Best Mini PC for a Firewall: OPNsense and pfSense Sizing

A dedicated firewall is one of the most satisfying homelab upgrades you can make. Swap your ISP's all-in-one router for a small x86 box running OPNsense or pfSense and you get proper firewall rules, VLANs for smart-home gear, a VPN server, DNS filtering and graphs that show exactly what your network is doing. The catch is choosing the hardware. Multi-port mini PCs range from palm-sized quad-core boxes to ten-port machines with 10GbE, and it is easy to overspend or, worse, buy something that bottlenecks your internet connection. This guide walks through how to size the best mini PC for a firewall, using the projects' own documentation as the baseline.

• Architecture: both OPNsense and pfSense need a 64-bit x86-64 (amd64) CPU, so Arm boards such as the Raspberry Pi are out
• RAM rule of thumb: each firewall state uses about 1 KB of RAM, so 1 million states needs roughly 1 GB on top of the operating system
• Recommended baseline: OPNsense recommends a 1.5 GHz multi-core CPU, 8 GB of RAM and a 120 GB SSD for full functionality
• Biggest bottleneck: Netgate says NIC quality matters as much as CPU, and Intel network controllers deliver more throughput at lower CPU load

Quick Picks: Which Mini PC Firewall Tier Fits You?

• Best starter tier: a fanless low-power quad-core mini PC with 4 x Intel 2.5GbE ports, 8 GB of RAM and a small NVMe SSD. Ideal for gigabit-class fiber, a few VLANs and WireGuard
• Best for intrusion detection: a six-core-or-better mini PC with 16 GB of RAM and Intel 2.5GbE ports, so Suricata or Snort has CPU and memory headroom
• Best for multi-gig and homelab routing: a mini PC with SFP+ 10GbE ports plus 2.5GbE ports, like the ten-port Qotom Q51551UT that ServeTheHome reviewed on October 22, 2026
• Best for running more than a firewall: a mini PC with 32 GB or more of RAM running Proxmox, with the firewall in a virtual machine and dedicated NICs passed through

What Are the Minimum Hardware Requirements for OPNsense and pfSense?

Both projects publish requirements, and they are modest. Netgate's documentation lists the pfSense minimum for non-Netgate hardware as a 64-bit amd64-compatible CPU, 1 GB or more of RAM, an 8 GB or larger disk, one or more compatible network cards, and a bootable USB drive for installation. Netgate is quick to add that the minimum is not suitable for every environment.

OPNsense breaks its guidance into tiers:

• Minimum: a 1 GHz dual-core CPU and 3 GB of RAM, enough for all standard features that do not need disk writes, installed from a nano image on a 4 GB or larger SD or CF card
• Reasonable: a 1 GHz dual-core CPU, 4 GB of RAM and a 40 GB SSD, where every feature works but perhaps not with many users or high loads
• Recommended: a 1.5 GHz multi-core CPU, 8 GB of RAM and a 120 GB SSD, which fits most use cases

Treat these as floors, not targets. Any current multi-port mini PC clears them easily, and the real decisions are about network ports, memory headroom and which extra services you plan to run.

Why Can't a Raspberry Pi Run OPNsense or pfSense?

Both projects are built on FreeBSD for x86-64, and OPNsense's documentation states plainly that it is available for the amd64 architecture only. That rules out the Raspberry Pi and most Arm single-board computers for these two distributions. A Pi can still handle network jobs such as DNS filtering, and there are other router operating systems that target Arm hardware, but if you specifically want OPNsense or pfSense, budget for an x86 mini PC. If you are weighing the two platforms for broader home-server duty, our Raspberry Pi vs mini PC home server guide covers the trade-offs.

How Much Throughput Does a Firewall Mini PC Need?

Start with your internet speed, then add headroom for internal routing between VLANs. OPNsense's sizing table maps throughput to hardware tiers: 11 to 150 Mbps for its minimum spec, 151 to 350 Mbps for reasonable, and 350 to 750-plus Mbps for recommended. Those figures are based on the project's original modest reference hardware, and current mini PC chips are far quicker than a 1.5 GHz baseline, but they illustrate an important point: throughput scales with the hardware, and the feature set you enable changes the math.

Packet size matters more than most buyers expect. Netgate's sizing guide gives an example of a firewall handling 500,000 packets per second:

• 64-byte packets: 244 Mbps
• 500-byte packets: 1.87 Gbps
• 1,000-byte packets: 3.73 Gbps
• 1,500-byte packets: 5.59 Gbps

In other words, the same box that easily routes large downloads can struggle with floods of tiny packets from gaming, VoIP or busy smart-home devices. Real traffic is a mix, which is why Netgate publishes IMIX results for its own appliances alongside maximum-size iperf3 numbers. When you compare mini PCs, look for packets-per-second or IMIX-style results in reviews, not just a single gigabit download test.

Why Do Intel NICs Matter So Much for a Firewall?

This is the single most important buying tip in this guide. Netgate's documentation states that inexpensive, low-end network cards consume significantly more CPU than better-quality cards such as Intel, and that pairing a slow CPU with a good NIC improves throughput significantly, while a faster CPU does not proportionally help a poor NIC. OPNsense's documentation agrees, noting that Intel chipset NICs deliver higher throughput at reduced CPU load and are reliable on its FreeBSD base.

In practice, that is why the multi-port mini PCs most often recommended for firewall duty use Intel controllers. Three to check for on a spec sheet:

• Intel I226-V: the current mainstream 2.5GbE controller, which also runs at 1GbE and slower speeds
• Intel X710 family: a mature 10GbE SFP+ controller that accepts 1GbE or 10GbE modules, including fiber optics
• Intel X540: an older 10GBase-T copper controller that supports 10GbE and 1GbE but not the intermediate 2.5 or 5 Gbps NBASE-T speeds, as ServeTheHome points out in its Qotom review

Also check how the ports connect internally. ServeTheHome found that on the Qotom Q51551UT, each 2.5GbE port has a PCIe Gen2 x1 link and two of its 10G ports share 12 Gbps of upstream bandwidth, so not every port can run flat out at once. For most home networks that is fine, but it matters if you plan to route multi-gig traffic between several ports at the same time.

How Much RAM Does an OPNsense or pfSense Firewall Need?

The core firewall is light. The state table, which tracks every active connection, is the main variable. Both projects put each state at about 1 KB of RAM, and Netgate's worked examples show:

• 100,000 states (50,000 connections): about 97 MB
• 1,000,000 states (500,000 connections): about 976 MB
• 8,000,000 states (4,000,000 connections): about 7,800 MB

Each connection consumes two states, one entering and one leaving the firewall, and the operating system needs at least another 175 to 256 MB on top. A typical home rarely gets near a million states, which is why 8 GB is plenty for most people. The memory jump comes from packages. Netgate says Snort and Suricata intrusion detection need 1 GB as a minimum and some configurations need 2 GB or more, not counting the operating system and states. OPNsense flags its Squid caching proxy and busy captive portals as the other features with a big impact on sizing. If you plan on intrusion prevention, 16 GB gives comfortable room.

Does a Firewall Mini PC Need AES-NI for VPN Speed?

If you run a VPN, yes, hardware crypto support is important. Netgate's documentation says VPN encryption is CPU-intensive and that the primary sizing question is VPN throughput, not the number of connected users. For IPsec, AES-GCM can be accelerated by the AES-NI instructions found in modern x86 CPUs, and Netgate notes IPsec is generally faster than OpenVPN because of lower per-packet overhead. Any current Intel or AMD mini PC supports AES-NI, but it is worth confirming on very old or ultra-budget models.

Should You Run Your Firewall in Proxmox?

Many homelabbers run OPNsense or pfSense as a virtual machine on a larger mini PC, alongside containers for Home Assistant, media servers or backups. That approach works well if the box has enough cores, generous RAM and spare NICs you can pass through directly to the firewall VM. ServeTheHome positions the Qotom Q51551UT, with its Core Ultra 5 125H, up to 96 GB of DDR5 in its test and ten network ports, for exactly that mix of firewall, edge and Proxmox duty.

The trade-off is resilience: when you reboot the host for updates, your whole network goes down with it. A small dedicated firewall plus a separate server is simpler to maintain. If you go the virtualization route, keep remote access in mind, and our IP KVM buying guide explains how to reach a headless box when the network is the thing you broke.

What Else Should You Check Before Buying?

• Storage: a small SSD is plenty. OPNsense recommends 120 GB for full functionality, and logging or a caching proxy are the main reasons to go bigger
• Cooling: fanless boxes are silent, but they rely on airflow around the chassis. ServeTheHome notes the Qotom uses a low-profile blower and is designed to sit on its side or on a VESA mount
• Serial console: an RJ45 or USB serial console port makes recovery much easier if you misconfigure an interface
• Power: check the adapter rating and idle draw, since a firewall runs 24/7
• Turnkey option: both projects point buyers who want a supported appliance to their partners, such as Netgate's own hardware or the vendors on OPNsense's partner page

The Bottom Line on Choosing a Firewall Mini PC

For most homes, the best mini PC for a firewall is not the most powerful one. It is an x86 box with genuine Intel network controllers, at least four ports at 2.5GbE, 8 GB of RAM and AES-NI, sized for your internet plan with headroom for VLAN routing. Step up to 16 GB and more cores if you want intrusion detection, and look at SFP+ 10GbE models only when your fiber service or internal network truly needs multi-gig. Get the NICs right and almost everything else follows. Explore more hardware guides in our mini computers coverage.

Sources: OPNsense hardware sizing documentation — accessed October 26, 2026; Netgate pfSense minimum hardware requirements — updated August 26, 2025; Netgate pfSense hardware sizing guidance — updated December 16, 2025; ServeTheHome Qotom Q51551UT review — October 22, 2026.