Frame Time Explained: The Real Measure of Smoothness
"I have 120 FPS but it doesn't feel smooth!" — If that sounds familiar, you need to understand frame time, not just FPS.
Why High FPS Can Still Feel Choppy
FPS (Frames Per Second) only tells you the average number of frames rendered per second. But here's the problem:
✅ Smooth 60 FPS
16.6ms, 16.6ms, 16.6ms, 16.6ms...
Each frame takes equal time
❌ Stuttery "60 FPS"
8ms, 8ms, 50ms, 8ms, 8ms...
One long frame = visible stutter!
Both scenarios average 60 FPS, but one feels terrible. Frame time reveals the truth.
Understanding the Metrics
FPS (Frames Per Second)
What it is: Average number of frames rendered per second
Formula: FPS = 1000 / Frame Time (ms)
Limitation: Hides stutters and inconsistencies
Frame Time (ms)
What it is: Time to render each individual frame in milliseconds
Why it matters: Shows the actual smoothness of each frame
What to look for: Spikes indicate stutters
1% Lows (and 0.1% Lows)
What it is: The worst 1% of frame times, converted to FPS
Why it matters: Shows how bad the worst stutters are
Healthy ratio: 1% lows should be at least 60-70% of average FPS
120 FPS / 90 1% Low
120 FPS / 60 1% Low
120 FPS / 30 1% Low
Frame Pacing
What it is: How evenly spaced frames are delivered
Perfect pacing: Each frame displays for exactly the same duration
Bad pacing: Frames display for varying durations, causing judder
Tools to Measure Frame Time
CapFrameX
Best for: Detailed analysis & comparisons
- Records frame times to CSV
- Creates beautiful graphs
- Compares multiple sessions
- Free & open source
RTSS (RivaTuner)
Best for: In-game overlay
- Real-time frame time graph
- Works with any game
- Frame rate limiter built-in
- Comes with MSI Afterburner
In-Game Options
Best for: Quick checks
- Steam: Settings → In-Game → FPS Counter
- NVIDIA: Alt+R for performance overlay
- AMD: Alt+R for metrics overlay
- Many games have built-in options
How to Interpret Frame Time Graphs
Healthy Graph
- Flat, consistent line
- No major spikes
- Frame times close to target (16.6ms for 60 FPS)
Signs of Problems
- Regular spikes: Could be background process, driver, or V-Sync issue
- Gradual increase: Memory leak or thermal throttling
- Random large spikes: Shader compilation, asset loading, or storage issue
- Constantly unstable: CPU bottleneck or badly optimized game