Video File Size Calculator: Estimate Size by Bitrate & Duration (2026)
Learn exactly how video file size is calculated, use our reference tables for 720p to 4K at every duration, and discover how to compress videos to your target size on macOS.
Video File Size Calculator: Estimate Your File Size Before You Export
If you have ever exported a video only to find it is far too large to send or upload, you are not alone. Knowing how to estimate video file size before you hit export saves time, storage, and upload headaches. This guide gives you the formula, reference tables, bitrate recommendations by platform, and practical tools to hit your target file size every time.
How Video File Size Is Calculated
Video file size comes down to one straightforward formula:
File Size (MB) = Bitrate (Mbps) × Duration (seconds) ÷ 8
Breaking that down:
- Bitrate is the amount of data used per second of video, measured in megabits per second (Mbps)
- Duration is the length of the video in seconds
- Dividing by 8 converts megabits to megabytes (since 1 byte = 8 bits)
Quick Example
A 10-minute video at 8 Mbps:
- 10 minutes = 600 seconds
- 8 Mbps × 600 ÷ 8 = 600 MB
That formula only covers the video stream. Add audio on top. A stereo AAC audio track at 128 kbps adds roughly 1 MB per minute, which is negligible for longer videos but worth noting for short clips.
The Manual Video Bitrate Calculator
You can flip the formula to solve for bitrate when you already know your target file size and duration:
Bitrate (Mbps) = Target File Size (MB) × 8 ÷ Duration (seconds)
So if you want a 5-minute video to land under 500 MB:
- 5 minutes = 300 seconds
- 500 × 8 ÷ 300 = ~13.3 Mbps
Keep that number in mind when you set your export settings.
Key Factors That Determine Video File Size
The formula gives you the math, but five variables drive what bitrate you actually need.
1. Resolution
Resolution is the pixel count of each frame. More pixels means more data to store. A 4K frame (3840 × 2160) contains roughly 8.3 million pixels compared to 2.1 million in 1080p — four times as many. All else equal, 4K footage requires four times the bitrate of 1080p to achieve equivalent visual quality.
Common resolutions and their pixel counts:
| Resolution | Pixels | Relative Data |
|---|---|---|
| 720p (1280×720) | ~922K | 1× |
| 1080p (1920×1080) | ~2.1M | ~2.3× |
| 1440p (2560×1440) | ~3.7M | ~4× |
| 4K (3840×2160) | ~8.3M | ~9× |
2. Frame Rate
Frame rate (fps) multiplies the data requirements directly. A 60fps video contains twice as many frames per second as 30fps, so it needs roughly double the bitrate to maintain the same per-frame quality. Common frame rates and their impact:
- 24 fps — cinematic look, smallest file size
- 30 fps — standard for most online content
- 60 fps — smooth motion for gaming and sports, larger files
- 120 fps — slow-motion capture, very large files
3. Bitrate
Bitrate is the single biggest lever for file size control. Higher bitrate = better quality + bigger file. The right bitrate depends on resolution, frame rate, and content complexity. A video with lots of motion (sports, action) needs more bitrate than a static talking-head recording at the same resolution.
4. Codec
The codec is the compression engine. Modern codecs like H.265 and AV1 can deliver the same visual quality as H.264 at roughly half the bitrate, cutting file size in half. More on codecs below.
5. Audio
Audio adds to the total but is usually a small fraction of video file size. Typical audio bitrates:
- 96 kbps — voice/podcast quality
- 128 kbps — standard stereo
- 192–256 kbps — music-heavy content
- 320 kbps — high-fidelity audio
For a 1-hour video, 128 kbps audio adds roughly 58 MB — noticeable in small clips but minor compared to a 4K video stream.
Reference Table: Typical File Sizes by Resolution and Duration
These figures assume H.264 encoding at typical recommended bitrates and stereo AAC audio at 128 kbps. Actual sizes vary by content complexity and encoder settings.
| Resolution | Bitrate Used | 1 min | 5 min | 10 min | 30 min | 1 hour |
|---|---|---|---|---|---|---|
| 720p (30fps) | 5 Mbps | ~38 MB | ~188 MB | ~375 MB | ~1.1 GB | ~2.2 GB |
| 1080p (30fps) | 8 Mbps | ~60 MB | ~300 MB | ~600 MB | ~1.8 GB | ~3.6 GB |
| 1080p (60fps) | 12 Mbps | ~90 MB | ~450 MB | ~900 MB | ~2.7 GB | ~5.4 GB |
| 4K (30fps) | 35 Mbps | ~263 MB | ~1.3 GB | ~2.6 GB | ~7.9 GB | ~15.8 GB |
| 4K (60fps) | 53 Mbps | ~398 MB | ~2.0 GB | ~3.98 GB | ~11.9 GB | ~23.9 GB |
These are H.264 estimates. H.265/HEVC at the same visual quality will produce files roughly 50% smaller. AV1 can go even smaller — see the codec section below.
For practical advice on cutting these numbers down, see our guide on how to reduce video file size.
Bitrate Recommendations by Use Case
Different destinations require different bitrates. Sending a 4K master to YouTube is very different from attaching a clip to an email.
YouTube Upload Bitrate Settings
YouTube re-encodes every video you upload, so your source file should be high quality. YouTube's own recommended bitrates for standard frame rates (24, 25, 30 fps):
| Resolution | Recommended Bitrate |
|---|---|
| 720p | 5–7.5 Mbps |
| 1080p | 8–12 Mbps |
| 1440p (2K) | 16 Mbps |
| 4K | 35–45 Mbps |
For high frame rates (48, 50, 60 fps), multiply by roughly 1.5×. Read our full YouTube video optimization guide for more settings.
Social Media Platforms
Social platforms are aggressive with re-compression, so there is little benefit to uploading at maximum bitrate. Target these ranges:
Instagram (Reels and Stories)
- Recommended: 3.5–5 Mbps at 1080p, 30fps
- Max file size: 4 GB, but aim well under 500 MB for fast uploads
TikTok
- Recommended: 2–5 Mbps at 1080p, 30fps
- Keep exports under 287.6 MB (TikTok's current limit)
Twitter/X
- Max file size: 512 MB for standard accounts
- Recommended: 5 Mbps at 1080p or 2.5 Mbps at 720p
- See our dedicated guide: compress video for Twitter
- Recommended: 5 Mbps at 1080p
- Max file size: 5 GB
Email Attachments
Email is the most restrictive destination. Most mail servers cap attachments at 10–25 MB, and many corporate environments are stricter.
| Target Size | Approach |
|---|---|
| Under 10 MB | 720p at 1–2 Mbps, 1–2 minutes max |
| Under 25 MB | 1080p at 3–4 Mbps, 1 minute max |
| Anything longer | Use a file sharing link instead |
Archive and Long-Term Storage
For archiving originals, prioritize quality over file size. Use high bitrates with H.265 to future-proof your library while keeping storage costs reasonable:
- 1080p archive: 15–20 Mbps with H.265
- 4K archive: 50–80 Mbps with H.265 (roughly half the size of equivalent H.264 files)
- Lossless: ProRes or DNxHR for source preservation before compression
How Codecs Affect File Size: H.264 vs H.265 vs AV1
The codec you choose is the most impactful decision after resolution and bitrate. Two videos with identical bitrates can look very different quality depending on the codec — and two videos at the same visual quality can have very different file sizes.
H.264 (AVC) — Universal Compatibility
H.264 is the most widely supported codec in the world. Every browser, device, and platform plays it. It is the safe default when compatibility matters most.
- File size: Baseline — largest of the three
- Compatibility: Virtually universal
- Encoding speed: Fast
- Best for: Email, broad distribution, legacy device support
H.265 (HEVC) — Half the Size, Same Quality
H.265 delivers the same visual quality as H.264 at roughly 40–50% smaller file sizes. A 4K video that is 10 GB in H.264 can drop to around 5 GB in H.265 at matching quality. The trade-off is that older hardware may not play it smoothly.
- File size: ~50% smaller than H.264 at equal quality
- Compatibility: Good on devices from 2016 onward, limited on older browsers
- Encoding speed: Slower than H.264 (Apple Silicon hardware encoding makes this fast on Mac)
- Best for: 4K content, archive storage, Apple device delivery
For a deeper comparison, see our guide on AV1 vs H.265.
AV1 — The Most Efficient Royalty-Free Codec
AV1 is developed by the Alliance for Open Media and is completely royalty-free. It compresses up to 30% better than H.265 and is increasingly supported by browsers and streaming platforms.
- File size: ~30% smaller than H.265, ~60% smaller than H.264 at equal quality
- Compatibility: Growing — supported by Chrome, Firefox, YouTube, Netflix
- Encoding speed: Slowest of the three (hardware acceleration is improving rapidly)
- Best for: Web streaming, future-proof archiving, large-scale distribution
Codec Comparison at a Glance
| Codec | Relative File Size | Compatibility | Speed |
|---|---|---|---|
| H.264 | 100% (baseline) | Excellent | Fast |
| H.265 / HEVC | ~50% | Good | Medium |
| AV1 | ~35% | Growing | Slow |
How to Reduce Video File Size Without Losing Quality
Knowing the formula is one thing — actually hitting your target size is another. Here are the most effective techniques, ranked by impact.
1. Switch to a More Efficient Codec
Going from H.264 to H.265 can cut your file size in half with no visible quality loss. This is the highest-leverage change you can make. Read our full breakdown on compress video without losing quality.
2. Lower the Bitrate Using Variable Bitrate (VBR)
Variable bitrate encoding allocates more bits to complex scenes (fast motion, fine detail) and fewer to simple scenes (static shots, talking head). This produces smaller files than constant bitrate (CBR) at equivalent average quality.
3. Reduce Resolution for the Target Platform
If your final destination is social media or mobile, exporting at 1080p instead of 4K can cut your file to one quarter of the size with no visible difference on a phone screen.
4. Lower the Frame Rate When Appropriate
For non-action content — interviews, tutorials, presentations — dropping from 60fps to 30fps halves the data requirements with minimal perceptible quality difference.
5. Trim Audio Bitrate
For voice-primary content, 96 kbps audio is indistinguishable from 192 kbps to most listeners. Cutting audio bitrate saves proportionally more on short clips.
For platform-specific workflows, see our guide on best video compression practices.
Using Compresto to Hit Your Target File Size on macOS
For Mac users, Compresto is the fastest way to compress videos to a specific file size without manual trial and error.
Compresto works on both Intel and Apple Silicon Macs and uses hardware-accelerated encoding for fast processing. Here is how the workflow looks in practice:
- Drag and drop your video file (or entire folder) into Compresto
- Choose your target format — H.264, H.265, or the output quality level
- Set your target — either a quality level or target file size
- Compresto processes the file using optimized encoding settings, leveraging Apple Silicon's hardware encoder where available
- Review the result — the compressed file sits alongside the original with a clear size comparison
Features that make Compresto practical for regular use:
- Folder Monitoring — automatically compresses new files added to a watched folder
- Drop Zone — system-wide drag-and-drop target without opening the full app
- Batch processing — compress an entire project folder at once
- Lossless reference — see exactly how much size you saved per file
If you regularly share videos for work, post to social media, or archive large libraries, Compresto removes the guesswork from the file-size calculation problem entirely.
Frequently Asked Questions
How do I calculate video file size manually?
Use the formula: File Size (MB) = Bitrate (Mbps) × Duration (seconds) ÷ 8. Multiply your bitrate (in megabits per second) by the video length in seconds, then divide by 8 to convert bits to bytes. Add a small amount for audio (roughly 1 MB per minute at 128 kbps stereo).
What is a good bitrate for 1080p video?
For YouTube and general distribution, 8–12 Mbps at 30fps is the standard recommendation for 1080p H.264. If you use H.265, you can achieve equivalent quality at 4–6 Mbps, cutting file size roughly in half.
Why does my exported video not match the size I calculated?
Several factors cause discrepancies: your encoder may use variable bitrate (which averages differently from the peak), containers add metadata overhead, and audio bitrate adds to the total. The formula gives a reliable estimate, not an exact figure. Actual files are typically within 10–15% of the calculated size.
How much does the codec affect file size?
Significantly. At equal visual quality, H.265 produces files roughly 50% smaller than H.264, and AV1 can reduce them by up to 60%. This is why modern streaming platforms have moved toward H.265 and AV1 — the bandwidth savings at scale are enormous.
What is the easiest way to reduce video file size on a Mac?
Compresto is the simplest option — drag in your video, pick your output quality, and the app handles codec selection and encoding settings automatically. For manual control, you can also use tools like HandBrake or FFmpeg with custom bitrate parameters. Learn more about file transfer time calculation to understand how smaller files affect your upload speed.
Understanding how video file size is calculated puts you in control of every export. Whether you are estimating size before you shoot, choosing the right bitrate for a platform, or compressing a library of existing footage, the formula and reference tables above give you a solid starting point.
For Mac users who want to skip the manual math, download Compresto at compresto.app and start hitting your target file sizes in seconds.