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For a new mini PC running a basic home router or firewall, choose 4 GB of RAM as a practical floor and 8 GB as the safer buying target. OPNsense lists 3 GB as a minimum for a restricted standard-feature configuration, 4 GB as reasonable for standard features, and 8 GB as recommended for most use cases. Netgate lists at least 1 GB as the minimum for third-party pfSense hardware, but that figure is a platform minimum rather than a universal recommendation. Optional packages, unusually large connection-state tables, and other services can push requirements higher.
RAM recommendations at a glance
There is no single RAM number that fits every mini PC router. The operating system, enabled packages, connection count and whether the box runs anything besides routing all matter. Use this table to separate a documented minimum from a sensible purchase target.
| Use case | RAM to consider | How to interpret it |
|---|---|---|
| OPNsense, restricted standard features | 3 GB minimum | OPNsense describes this as the minimum for standard features that do not need disk writes. It is not a general headroom target. |
| OPNsense, ordinary home routing and firewalling | 4 GB reasonable | A practical baseline for standard features at ordinary loads, without implying a performance guarantee. |
| OPNsense, most new builds | 8 GB recommended | OPNsense recommends this capacity for most use cases. It does not guarantee a particular throughput, VPN rate or IDS/IPS result. |
| pfSense on third-party hardware | At least 1 GB minimum | Netgate’s published minimum is a boot-and-run floor. Packages and large state tables can require more. |
| Proxy, captive portal, intrusion detection/prevention or very large state tables | No universal figure established | Size the complete workload, then confirm the mini PC’s maximum supported memory. |
These figures come from the vendors’ hardware documentation: OPNsense hardware sizing and Netgate’s pfSense minimum hardware requirements.
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Why the answer changes between OPNsense and pfSense
Software vendors use different definitions for minimum, reasonable and recommended hardware. A minimum usually means the software can install and operate with a narrowly defined configuration. It does not mean every package, traffic pattern or connection table will fit comfortably.
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OPNsense publishes three useful tiers instead of one number. Its 3 GB minimum applies to standard features without disk-write requirements; 4 GB is described as reasonable for standard features; and 8 GB is recommended for most use cases. The documentation also warns that load and feature selection affect sizing, so an 8 GB appliance should not be read as a promise of a particular line rate.
Netgate’s pfSense documentation gives a lower headline number: at least 1 GB for third-party hardware. Treat that as the minimum for the platform, not as advice that every pfSense installation should be built with only 1 GB. Netgate specifically notes that packages and large state tables increase memory needs.
How connection states consume RAM
A firewall tracks active flows in a state table. Every TCP session, UDP flow and similar tracked connection consumes memory for its state record. OPNsense estimates about 1 kB of RAM per state-table entry. At that rate, 1,000 entries occupy about 1 MB; 100,000 entries would represent roughly 100 MB before accounting for other data structures and the rest of the operating system. Hundreds of thousands of simultaneous states therefore need materially more memory than a quiet home network.
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pfSense uses the same basic sizing concern. Netgate explains that its default state-table size is calculated from a share of available RAM and uses an estimate of about 1 kB per state entry on its official product and hardware information page: pfSense hardware and appliances. The configured maximum is not the same as actual usage, but reducing available RAM reduces the margin for a large table and for packages running alongside it.
Choose RAM by workload, not by WAN speed alone
Internet speed is only one part of a firewall build. The cited sizing guidance does not provide a formula that converts a 500 Mbps or 1 Gbps connection directly into a RAM requirement. CPU architecture and clock speed, network-interface quality, storage, encryption workload, driver support and enabled services can be just as important.
Basic routing and firewall rules
If the mini PC will perform NAT, DHCP, DNS forwarding and ordinary firewall rules for a home or small office, 4 GB is a defensible OPNsense baseline. When buying a new unit, 8 GB gives more room for updates and additional standard features and aligns with OPNsense’s recommendation for most use cases. Existing 4 GB hardware does not need an automatic upgrade merely because 8 GB is available.
VPN and encrypted traffic
VPN performance is not determined by RAM alone. Encryption often makes CPU capability and hardware acceleration more influential than adding memory. Do not infer a guaranteed VPN speed from an 8 GB specification; the available guidance does not establish such a benchmark.
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Proxy and captive portal services
OPNsense specifically identifies proxy and captive-portal workloads as factors that should be considered in sizing. These services add working data beyond the core packet-filtering path. If either is central to the design, start from the 8 GB tier and verify real memory use under the expected client and policy load rather than treating 4 GB as a fixed rule.
Intrusion detection, prevention and monitoring packages
Optional inspection and monitoring packages can be memory-intensive. Netgate’s general pfSense guidance calls out packages such as Snort and ntop as examples that may need substantial memory. The available documentation does not assign a reliable extra-GB allowance to each package, so a claim such as add exactly 2 GB for a particular package would be unjustified. Plan for the combined package set, rule database, logs and connection table, then leave headroom.
Running other services on the same mini PC
A firewall appliance that also hosts file sharing, containers, a virtual machine, media services or development tools is no longer a firewall-only workload. Account for those applications separately. If isolation and predictable firewall behavior matter, using a dedicated appliance avoids having unrelated processes compete for the same RAM.
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The following decision path keeps the vendor figures in context:
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- Identify the firewall software. For OPNsense, use 3 GB only as the documented minimum for its restricted standard-feature case, 4 GB as the practical baseline, and 8 GB as the normal new-build target. For pfSense, regard Netgate’s 1 GB figure as a minimum for third-party hardware.
- List every enabled feature. Include proxying, captive portal, intrusion detection or prevention, traffic analysis, extensive logging and any package that maintains large databases in memory.
- Estimate peak concurrent states. Use the busiest realistic period, not the number of devices alone. OPNsense’s approximately 1 kB-per-entry estimate shows why a six-device network can still create a large table if applications open many simultaneous flows.
- Add non-firewall workloads. Count virtual machines, containers and server applications that will share the box. Their memory demand is independent of the firewall minimum.
- Select a supported capacity. Prefer a mini PC that accepts a replaceable module if you expect the workload to grow. Do not buy a memory size that the motherboard or firmware cannot address.
How much headroom should a new purchase have?
For a straightforward OPNsense router, 4 GB can keep the purchase cost and power footprint down when the feature set is stable. An 8 GB model is the more forgiving choice for most new installations because it follows OPNsense’s recommended tier and leaves room for additional standard features, larger state tables and software updates.
For pfSense, do not interpret the 1 GB third-party minimum as a buying target. A buyer can use the OPNsense 8 GB recommendation as a conservative reference point for a new, general-purpose appliance, but that is not a pfSense performance guarantee or an official pfSense requirement. The correct capacity still depends on packages, states and other services.
Moving to 16 GB can be reasonable only when the mini PC supports it and the workload justifies the extra capacity. The published guidance does not establish 16 GB as necessary for ordinary routing, nor does it provide package-by-package figures that would make 16 GB universally correct.
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Firewall sizing documents cannot tell you whether a particular mini PC accepts a specific module. Compatibility is a separate hardware decision. Complete these checks against the exact model manual or vendor specification:
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- Memory technology: confirm whether the system uses DDR3, DDR4 or another generation. A DDR4 module is not interchangeable with a DDR3 slot.
- Form factor: verify whether it takes a laptop-style SO-DIMM, a desktop DIMM or another module type.
- Slot layout: determine whether RAM is socketed, soldered or partly soldered, and whether there is one slot or two.
- Maximum capacity: check the manufacturer’s supported maximum and the maximum capacity per slot. A physically compatible module can still exceed firmware or chipset limits.
- Existing configuration: note the installed module’s capacity and specification before mixing modules. Matching the documented type and supported speed avoids an upgrade that fails to boot or falls back to an unexpected configuration.
- Upgrade access: confirm that opening the case does not conflict with the device’s warranty terms and that you can reach the memory without disturbing the storage or cooling system.
The phrase 8GB DDR4 SO-DIMM is a search description, not a universal part recommendation. Without the exact mini PC model, no particular module can be confirmed as compatible.
Appliance examples: shipped RAM is not a benchmark
Purpose-built appliances show that vendors ship different memory capacities for different designs. The OPNsense Shop listing for the DEC677 describes a 4 GB DDR3 configuration, while the DEC750 listing describes 8 GB DDR4. Netgate’s official product catalog also lists models with differing RAM amounts at its appliance page.
Those shipped capacities demonstrate that 4 GB and 8 GB are both used in real appliance configurations, but they are not independent performance tests. They do not prove a particular throughput, VPN rate, state-table limit or IDS/IPS capability. Compare the complete CPU, interface and storage design as well as RAM.
Signs that your current RAM capacity is the constraint
Use the firewall’s own memory and state-table monitoring during the busiest periods you expect. A capacity problem is more plausible when memory remains heavily committed while the state table is large, when adding a package causes instability, or when unrelated services compete with the firewall. Capture observations before changing hardware so you can distinguish a RAM shortage from CPU saturation, a driver problem, storage pressure or a configuration error.
If the system is stable with ordinary routing and has unused memory, adding RAM will not automatically increase WAN throughput. Conversely, increasing RAM cannot compensate for an underpowered CPU, poor network interfaces or insufficient storage. Upgrade the component that limits the observed workload.
A practical buying checklist
- Choose 4 GB when the plan is a basic OPNsense router/firewall with a controlled feature set and the mini PC is already available.
- Choose 8 GB for most new OPNsense purchases, for expected feature growth, or when you want more state-table and package headroom.
- Treat 1 GB on pfSense as Netgate’s third-party hardware minimum only; do not assume it covers packages or unusually large connection tables.
- For proxy, captive portal, intrusion detection/prevention, heavy monitoring or shared server workloads, size the complete application set and test peak behavior rather than applying a fixed add-on number.
- Before ordering an upgrade, verify the exact RAM generation, SO-DIMM or DIMM form factor, slot arrangement, soldering and supported maximum for the mini PC.
- Evaluate CPU, storage and network interfaces independently. RAM capacity alone is not a throughput specification.
Bottom line
For a mini PC used as a normal home router or firewall, 4 GB is a practical minimum and 8 GB is the safer all-purpose choice. OPNsense documents 3 GB minimum, 4 GB reasonable and 8 GB recommended for most use cases. pfSense’s 1 GB third-party minimum should be treated strictly as a floor. Once you add packages, large state tables or other services, calculate the workload and confirm the mini PC can accept the RAM you intend to install.
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