Slow Motion Frame Rate Calculator
Calculate the required frame rate to achieve desired slow motion factor at output fps. Enter values for instant results with step-by-step formulas.
Formula
Capture FPS = Output FPS x Slow Motion Factor
The required capture frame rate equals your timeline playback frame rate multiplied by the desired slow motion factor. The resulting clip duration equals the recording time multiplied by the same factor.
Worked Examples
Example 1: Water Splash at 8x Slow Motion
Problem: You want to film a water splash at 8x slow motion for a 24 fps timeline. The real action lasts 2 seconds. What frame rate and clip duration result?
Solution: Required capture rate = 24 fps x 8 = 192 fps\nRecording duration = 2 seconds\nTotal frames captured = 192 x 2 = 384 frames\nPlayback duration at 24 fps = 384 / 24 = 16 seconds\nMax shutter speed (180-degree rule) = 1/384\nLight needed: ~8x more than normal 24 fps shooting\nStorage multiplier: 8x normal rate
Result: Capture at 192 fps | 384 frames | 16-second clip from 2-second capture
Example 2: Sports Replay at 120 fps
Problem: A sports camera captures at 120 fps and the replay timeline runs at 30 fps. How slow is the motion, and how long is a 5-second capture?
Solution: Slow motion factor = 120 / 30 = 4x\nRecording duration = 5 seconds\nTotal frames = 120 x 5 = 600 frames\nPlayback duration = 600 / 30 = 20 seconds\nTime per frame = 1000 / 120 = 8.33 ms\nShutter speed (180-degree) = 1/240\nStorage = 4x normal 30 fps footage
Result: 4x slow motion | 600 frames | 20-second clip from 5-second capture
Frequently Asked Questions
How does slow motion work and what frame rate do I need?
Slow motion works by capturing video at a higher frame rate than the playback rate, then playing back at the normal speed so each moment stretches over a longer time period. To calculate the required capture frame rate, multiply your desired playback frame rate by the slow motion factor. For example, if you want 4x slow motion in a 24 fps timeline, you need to capture at 96 fps (24 times 4). The more frames you capture per second, the smoother and more dramatic the slow motion effect becomes. Modern consumer cameras typically offer 60 to 240 fps, while professional cinema cameras can reach 960 fps or higher. Dedicated high-speed cameras used in scientific and industrial applications can capture millions of frames per second.
What is the 180-degree shutter rule and why does it matter for slow motion?
The 180-degree shutter rule states that your shutter speed should be set to double your frame rate for natural-looking motion blur. At 24 fps, this means a 1/48 shutter speed. For slow motion at 120 fps, you would use 1/240 shutter speed. This becomes critical at high frame rates because the extremely fast shutter speeds let in very little light, requiring significantly more lighting or wider apertures. A scene properly exposed at 24 fps with a 1/48 shutter would need approximately 5 times more light at 120 fps with a 1/240 shutter. Some cinematographers intentionally break this rule for slow motion, using a wider shutter angle (slower shutter speed) to introduce deliberate motion blur that makes the slow motion feel dreamier rather than hyper-crisp.
How much longer will my slow motion clip be compared to the recorded time?
The resulting clip duration equals the recording duration multiplied by the slow motion factor. If you record for 5 seconds at 4x slow motion, the resulting clip will be 20 seconds when played at normal speed. This relationship is straightforward: 2x slow motion doubles the duration, 8x slow motion makes a 3-second capture last 24 seconds. This has important implications for storytelling because slow motion clips take up significantly more timeline space. A 10-second high-speed capture at 10x slow motion produces 100 seconds of footage, nearly two minutes. Editors must plan carefully to use slow motion effectively without making sequences feel unnecessarily drawn out. Most slow motion shots in professional productions last only 3 to 8 seconds of playback time.
What are the lighting requirements for high-speed slow motion recording?
High-speed recording requires proportionally more light because the faster shutter speeds reduce each frame exposure time. At 24 fps with a 1/48 shutter, each frame receives approximately 20.8 milliseconds of exposure. At 240 fps with a 1/480 shutter, each frame gets only 2.08 milliseconds, which is 10 times less light per frame. You can compensate by opening the aperture wider, increasing ISO (at the cost of more noise), or adding more lighting. For indoor high-speed shooting, continuous LED panels are preferred over strobes because they provide constant illumination across all frames. When shooting at 1000 fps or higher, professional HMI or LED arrays providing thousands of watts are typically required. Outdoor daylight provides ample illumination for most consumer high-speed modes up to 240 fps.
Does resolution decrease at higher frame rates?
Yes, most cameras reduce resolution as frame rate increases because the sensor readout speed and data processing pipeline have bandwidth limitations. A camera that records 4K at 30 fps might drop to 1080p at 120 fps and 720p at 240 fps. This occurs because the sensor cannot read and process the full resolution at higher speeds, so it either skips lines, uses a smaller crop of the sensor, or bins adjacent pixels together. Professional cinema cameras like the RED V-RAPTOR or Phantom Flex maintain higher resolutions at higher frame rates through faster sensor designs and more powerful processors. When planning slow motion shots, always verify the actual resolution your camera delivers at your target frame rate, as marketing materials may emphasize the maximum frame rate without clarifying the resolution reduction.
What is the rolling shutter effect and is it worse in slow motion?
Rolling shutter occurs because CMOS sensors read each line of pixels sequentially from top to bottom rather than capturing the entire frame simultaneously. This creates a time offset between the top and bottom of each frame, causing fast-moving subjects or rapid camera movements to appear skewed or wobbly. The rolling shutter effect can be either better or worse in slow motion depending on the camera implementation. If the camera uses a sensor crop for high frame rates, the readout time per frame may actually decrease, reducing rolling shutter artifacts. However, if the camera reads the full sensor with line-skipping, rolling shutter remains proportional. Global shutter sensors, which capture all pixels simultaneously, eliminate this problem entirely and are increasingly available in cinema cameras specifically designed for high-speed work.