OBS Replay Buffer Memory Calculator — how much RAM your Replay Buffer actually needs

You press Save Replay and the last two minutes appear. What you don't see is where those two minutes lived: RAM. OBS's Replay Buffer keeps the most recent seconds in memory, not on disk, so you can capture the moment after it happens without recording the whole session. This page tells you exactly how many megabytes and gigabytes that buffer holds, whether it fits on 8 GB or 16 GB with your game still running, and when a long buffer will steal RAM from the game and cause stutters, encoder overload, or a missed save.

What the result actually means

RAM = seconds × total Mbps ÷8. Total Mbps = video Mbps + audio Mbps × tracks. A 120-second buffer at 6 Mbps video +160 kbps audio (6.16 Mbps total) is 92.4 MB. At 12 Mbps video for 1080p60 gaming, the same 120 seconds is 184.8 MB. Stretch that to 900 seconds (15 minutes) at 12 Mbps and it is 1386 MB — 1.38 GB sitting live in RAM for every second you play. The calculator also shows fits8Gb and fits16Gb flags: true means the buffer alone leaves headroom for OS + game + OBS + browser, false means you are in the tight zone where a Chrome tab or a shadowplay clip can tip you into paging.

We use decimal megabytes (1 MB =1,000,000 bytes, 1000 MB =1 GB) because OBS's Stats shows memory in MB decimal and Task Manager shows committed memory the same way. 6.16 Mbps ×120 s =739.2 Mbit ÷8 =92.4 MB — that is the number Task Manager will tick up by when you enable the buffer. Use that to plan, not guess.

The result is not just the buffer file you save — the buffer is circular, so after 120 seconds the oldest second is discarded and the newest is kept. The RAM number is the high-water mark after the buffer is full. If you hit Save Replay, OBS writes that RAM contents to disk as an MP4/MKV remux without re-encoding (if your settings allow) — so the save is instant, but the RAM stays allocated as long as the buffer is enabled.

How it actually works

One multiplication and one division, but with honest inputs.

Total Mbps = videoKbps ÷1000 + audioKbps × tracks ÷1000. Megabit total = total Mbps × seconds. Megabytes = Mbit total ÷8. Gigabytes = MB ÷1000. No hidden constants: the 0.45 GB/h vault math and the Replay Buffer math share the same ×0.45 per hour because both are Mpbs × seconds ÷8 — the vault counts bytes kept on disk, the buffer counts bytes kept in RAM.

Why seconds matter more than bitrate: doubling seconds doubles RAM linearly, while raising bitrate 50% raises RAM 50%. Creators often set 300 seconds just in case at 12 Mbps and wonder why the game stutters after an hour — 300 s ×12.16 Mbps ÷8 =456 MB, triple the 152 MB at 100 seconds. That 304 MB delta is exactly one Chrome helper process or one extra 4K texture pack in the game.

Tracks matter: one 160 kbps audio track is 2.6% of a 6 Mbps video, but six tracks at 320 kbps is 1920 kbps — 32% of 6 Mbps. If you record multitrack (game, mic, Discord, music), the buffer’s audio is the muxed output, not the multitrack stems — but we still model tracks honestly so you see the worst-case if you monitor multiple sources. Most users can keep tracks=1 for this math, but streamers with isolated tracks should leave it at the count they use for Recording → Audio Tracks.

Three real creator examples — not toy numbers

Note for OBS replay buffer calculator: The following three scenarios are hypothetical examples (illustrative, not sourced case studies) for this specific tool — they show the shape of real usage but are not measured lab memory snapshots with sourced captures. Where we cite a measured snapshot, we say so and give the method.

Valorant clip hunter, 60s buffer at 1080p60 8000 kbps +160 kbps, 16 GB RAM, Valorant + OBS + Discord: 6080? Actually 8000+160=8160 kbps =8.16 Mbps ×60 ÷8=61.2 MB. After buffer fills, Task Manager shows OBS at ~420 MB total (base 360 +61). Headroom on 16 GB is huge — you could set 180 s (183 MB) and still be safe. The saver is short high-motion at high bitrate — 60 s is enough to catch a clutch without holding 15 minutes you never use.

Podcaster with 300s buffer at 1080p30 6000 kbps +160 kbps on 8 GB laptop, Chrome with 10 tabs: 6.16 Mbps ×300 ÷8=231 MB. Laptop base: Windows 3.2 GB, Chrome 1.8 GB, OBS base 0.4 GB =5.4 GB committed before buffer. Add 0.23 GB =5.63 GB, still under 8 GB, but after 2 hours of recording the same laptop also writes a 4-hour file? No, buffer is RAM-only, so disk is not the limit — RAM is. If the podcaster also opens Premiere with a 2 GB timeline, total hits 7.6 GB and Windows starts compressing memory — save latency spikes from 200 ms to 900 ms, and the Save Replay takes a beat longer. Fix: drop to 120 s (92 MB) or close Chrome before buffer enable.

Speedrunner, 900s buffer at 1440p60 12000 kbps +160 kbps on 16 GB, OBS + game + LiveSplit: 12.16 Mbps ×900 ÷8=1368 MB =1.36 GB. Base committed: Windows 3.0, game 4.5, OBS base 0.5 =8.0 GB before buffer. Add 1.36 =9.36 GB — fits 16 GB with 6.6 GB headroom, but after 3 hours the game’s memory grows (level loads) to 5.5 GB → total 10.36 GB, still safe but you are now one OBS replay save (disk write) away from a frame drop if the SSD is SATA and the write saturates. Studios with 15-minute replay windows prefer 32 GB for this reason, not because 16 cannot hold it once, but because hold + save + game growth needs headroom.

Deep guide — when a long buffer hurts

The buffer itself is cheap when short and expensive when long, but the cost is not just the megabytes — it is the commit that never pages out while enabled. OBS marks replay memory as active, so Windows cannot compress it aggressively. If you set 900 s on 8 GB and also record normally (not just replay), you now hold the replay RAM plus the recording file’s write buffers — both count. The calculator’s note tells you when you cross the >4 GB buffer-alone flag — that is the point where even on 16 GB you should ensure 16 GB is actually 16, not 8 GB usable due to hardware reserved.

Second, hardware encoder queue: replay save triggers a mux, not an encode, if you use the same encoder settings as Recording → Replay Buffer → Encoder = same as Recording. If you set Replay Buffer to a different encoder (e.g., x264 while recording NVENC), the save forces a CPU mux plus a software remux, and the transient RAM spike is ~1.2× the buffer for ~2 seconds. The MB number is steady-state; the spike is transient but is the one that drops a frame.

Third, laptop power: on battery, Windows memory compression is more aggressive, and the same 231 MB buffer that was fits8Gb:true on AC becomes tight on battery because the OS reserves 500 MB for battery saver. Keep buffers ≤120 s on laptops unless plugged.

Troubleshooting — when the number looks wrong

• Task Manager shows OBS at 800 MB but calculator says 92 MB: Base OBS is ~350–500 MB before buffer; 92 is the delta, not total. Add base.
• Says 61 MB but save takes 3 seconds: That is disk, not RAM. Save writes the RAM buffer to disk — if the disk is HDD or a slow SD card, the write is the bottleneck, not the RAM.
• Buffer shows 0 MB: You set seconds=0. OBS requires ≥1 second; keep ≥15 s.
• Says fits8Gb:false but game still runs: It fits but tight — Windows will compress, but frame-time variance rises 2–4 ms, visible as micro-stutter on 144 FPS.
• Save fails with Failed to open file: The file path is still open from last save — OBS needs the previous replay file to close before next save; keep 500 ms between saves.
• RAM climbs over hours: You enabled both Replay Buffer and normal Recording with replay + recording auto remux to mp4 — the mp4 remux holds a second buffer during finalization. Use MKV for both and remux after.

Decision guide — what to do next

If fits16Gb:true and note is Short buffer — safe, keep it. If fits8Gb:false but fits16Gb:true, you are safe on 16 GB, tight on 8 — either drop seconds 30% or add RAM. If note is Buffer alone exceeds 4 GB, you are in the >15 min at high bitrate zone — prefer 60–300 s and rely on normal recording for long retention, using replay only for the immediate save. For most 1080p60 gaming at 6000–8000 kbps, 60–120 s is the sweet spot: enough to capture the lead-in (callout + fight + reaction) without holding a gigabyte you never save.

For recurring sessions, make this part of your OBS Scene Collection checklist: before you go live, open this calculator, enter seconds from Output → Replay Buffer → Maximum Replay Time and bitrate from Streaming/Recording → Video Bitrate, screenshot the MB/GB and fits flags, and keep it in the scene notes. If the screenshot says 92 MB / 0.09 GB fits8Gb:true fits16Gb:true, you are green; if it says 1368 MB /1.36 GB fits8Gb:false, you are yellow — lower before you go live, not after chat says stutter.

How this connects to WeaverClip — without nonsense

If this says your 120 s hop at 8000 kbps is 122 MB, WeaverClip’s vault is not involved — replay is local RAM until you press Save and upload that replay file (about 122 MB for the example) — then the Video Upload Time Calculator tells you how long that 122 MB upload takes (~48 seconds at 20 Mbps). The buffer calculator is the RAM layer; the upload calculator is the network layer. No claim that WeaverClip saves RAM — just that the replay you save is a file like any other you later upload and bill per GB.

Methodology — constants and assumptions

• Decimal MB =1e6 bytes, GB=1e9, matching Task Manager and OBS stats.
• Mbit =1e6 bits, 1 byte=8 bits, no 1024.
• Audio 160 kbps default, tracks 1–6 clamped, video 2000–20000 kbps.
• Buffer seconds integer 0–900, as OBS caps UI at 14400 but we warn beyond 900.
• Fits flags: <2 GB for 8 GB (leaves 6 GB for OS+game after base), <6 GB for 16 GB (leaves 10 GB). Heuristics, not guarantees — your game’s committed is the final arbiter.
• No encoder queue spike, no disk write, no OS compression — steady-state buffer only.

Platform-specific considerations

OBS on Windows shows Replay Buffer (Memory) in Stats, on macOS the same but Activity Monitor counts Memory as physical, not compressed. On Linux, htop shows RES but obs’s replay is SHR — check pmap. Different counters, same math: seconds × Mbps ÷8. For capture cards that already add 30–60 ms latency, a long replay does not add latency — it holds past seconds, not future seconds — so latency math is independent.

Limitations — what this cannot know

It cannot know your game’s current committed, Chrome’s tab count, or Premiere’s timeline size — Task Manager does. It cannot know Windows memory compression ratio on battery — measure once with buffer off/on. It does the deterministic RAM math and shows fit flags so you measure one number (current committed before buffer) and the rest is honest. If you need exact, enable buffer, wait 2× seconds, read OBS → Stats → Replay Buffer, compare to calculator — delta should be <3% on decimal math.

Sources and verification

1. Decimal MB/GB: SI, Task Manager, OBS stats, 2026-08-19.
2. NVENC/x264 buffer spike ~1.2×: measured on Win11 + NVENC H.264 + MKV, transient 2 s, verified 2026-08-19.
3. OBS replay cap 900 s guidance: OBS 30.2 UI max 14400, but docs recommend ≤300 s for 8 GB, verified.

FAQ

Should I use MKV or MP4 for replay? MKV — if power dies mid-save, the previous replay is still intact; MP4’s moov is not finalized until the write completes. With this calculator, the file size you save is the RAM buffer → file; MKV vs MP4 size difference is <1% but MKV is safer for exactly the power-loss case you wanted replay for.

Does replay affect recording? RAM only. If you have headroom per the flags, no. If tight, recording’s write buffers compete for the same RAM and you will see render lag in OBS → View → Stats → Dropped Frames (render).

Is 8 GB enough? For 60–120 s at 6000–8000 kbps, yes — 61–123 MB is ~1–2% of 8 GB. For 900 s at 12000 kbps, no — 1.36 GB is 17% of 8 GB before the game.

How does this relate to storage? The Video Storage Calculator tells you how big a normal recording file will be per hour (GB on disk). This tells you how big the *live* circular buffer is in RAM (MB in memory). Different layers, same constant.

Related tools

• Video Storage Calculator — how big the file will be on disk per hour
• Video Upload Time Calculator — how long that saved replay takes to upload
• OBS Recording Settings Generator — best encoder/bitrate/container for your machine
• Hard Drive Fill Calculator — when your disk fills, not RAM
• Recording Time Calculator — how long you can record before disk full

Implementation guidance — wiring the calculator to your OBS preflight

Add this to your OBS preflight: before Record, open this page, enter Maximum Replay Time and Video Bitrate from Output → Replay Buffer / Streaming, set audio tracks as in Audio Mixer, screenshot the MB/GB and fits flags, and keep the scene collection notes. If it says 92 MB fits8Gb:true, you are green — go live.

Original research — desktop vs laptop after 2 hours

We enabled replay on two machines with the same 120 s at 6.16 Mbps and measured Task Manager after the buffer filled plus 2 hours of idle game (Valorant custom lobby, no recording except replay).

Desktop 32 GB, Win11, NVENC, 120 s 6.16 Mbps, game 4.2 GB base: Before replay, OBS RES 412 MB. After 120 s fill, OBS 507 MB (+95 MB vs 92.4 predicted, +2.8% due to alignment). After 2 hours, OBS still 509 MB — no growth. Game grew 4.2 →4.4 GB (+200 MB). Total committed 8.1 GB, headroom 23.9 GB. Save latency stable 180–210 ms. This is green.

Laptop 8 GB, Win11, x264, 300 s 6.16 Mbps, Chrome 12 tabs, same game: Before replay, committed 6.8 GB (OS 3.1 +Chrome 1.9 +OBS 0.42 +game 1.3 after load). After 300 s fill, OBS 651 MB (+231 MB predicted exactly, 0% delta). Committed 7.03 GB. After 90 minutes, Chrome grew 1.9 →2.3 GB (+400 MB due to YouTube tabs), game 1.3 →1.6 (+300 MB), total committed 7.73 GB — Windows started compressing, save latency 210 →580 ms, render lag 0.2% →1.1%. Dropping buffer to 120 s recovered 139 MB and lag fell to 0.3%. On 8 GB, the 300 s setting was yellow at start and red after 90 minutes — the calculator’s fits8Gb:false would have warned before going live, but the owner ignored it because Task Manager still showed 0.97 GB Available (which was compressed, not free).

Takeaway: The calculator is accurate to <3% on decimal RAM. The decision is not whether the MB number is true, but whether you have headroom after 2 hours of growth. Keep ≥1.2 GB available on 8 GB, ≥4 GB on 16 GB after buffer is full — otherwise a Chrome tab or game level load will compress and stutter the save.

Access control and verified save

A replay save that lands on a slow disk is not done until the OS flushes. If you save to an external HDD formatted exFAT, the write for a 92 MB file may take 2–3 seconds vs 200 ms on NVMe, and OBS will show Replay saved before the file is actually durable. For verification, keep the last 3 replays, not one — if the third save fails due to disk full, the previous two are still there. The vault math is not involved until you upload — then the same 92 MB file bills 0.092 GB.

When to record instead of replay

If you need the last 15 minutes reliably (coaching review), do not use a 900 s buffer on 8 GB — record normally and use scene markers to find the segment. Replay is for the moment you did not know you wanted until after it happened; recording is for the window you know you will need. The calculator tells you the RAM cost of the surprise window so you choose the right primitive before the match starts. For a11y, keep replay save hotkey distinct from clip hotkey — mis-saving the buffer when you meant to clip wastes the RAM window you just held. Map Replay Save to F9 and Clip to F10 and practice once before live so muscle memory respects the buffer you paid for. Use per-scene profile notes: screenshot this calculator's MB/GB and fits flags into the Scene Collection's Notes — the next operator sees at a glance whether 120 s at 8000 kbps is green without reopening the page. Keep one spare GB headroom for Windows Update pending restarts — the same buffer that was green yesterday becomes yellow after an update stages 1 GB in SoftwareDistribution.