About the Slow Motion Calculator
This slow motion calculator shows exactly how slow your footage will play. Enter the frame rate you record at, the frame rate of your project or timeline, and how long the real action lasts, and it returns the slow-down factor, the playback speed as a percentage, how long the clip will run on screen, how many frames you capture and the shutter speed that gives natural-looking motion blur.
It is useful for filmmakers planning high-frame-rate shots, sports and wedding videographers, phone users trying 240 or 960 fps modes, and anyone deciding whether 60, 120 or 240 fps is enough. It also works backwards: enter the slow-down you want and it tells you the capture frame rate needed for your timeline.
The calculation assumes the footage is conformed (interpreted) so every captured frame is shown once at the playback rate — the cleanest form of slow motion with no frame blending or interpolation. Remember that high frame rates need short shutter speeds and therefore more light, and many cameras crop or reduce resolution in their fastest modes.
With the default inputs, the slow-down factor is 5 ×. Change any value above to recalculate instantly.
How to use the slow motion calculator
- 1Enter the frame rate you will record at.
- 2Choose your timeline or delivery frame rate.
- 3Enter how many seconds the real action lasts.
- 4Read the slow-down factor, playback speed and on-screen length.
- 5Optionally enter the slow-down you want to see the capture rate it requires.
Formula and method
When footage recorded at a high frame rate is conformed to a lower timeline rate, every captured frame is still shown once, but more slowly. The slow-down factor is therefore the capture rate divided by the playback rate, and the playback speed is its inverse as a percentage: 120 fps on a 24 fps timeline plays at 20% speed, five times slower than life.
The action’s on-screen length is its real length multiplied by the factor, and the number of frames recorded is real length × capture rate. The 180-degree shutter rule sets the exposure to half the frame interval, 1 ÷ (2 × capture fps), which gives the motion blur audiences perceive as natural. To reach a target slow-down, multiply it by the playback rate to get the capture rate you need.
- capture fps
- Frame rate the camera records at
- playback fps
- Frame rate of the edit timeline or delivery
- factor
- How many times slower than real life the footage plays
Worked examples
120 fps on a 24 fps timeline
120 ÷ 24 = 5, so the footage plays five times slower, at 20% speed. Ten seconds of action records 1,200 frames and fills 50 seconds of screen time. The 180° shutter is 1/240 s, and a 10× slow-down would need 240 fps.
240 fps jump on a 30 fps timeline
240 ÷ 30 = 8× slower, or 12.5% speed. A 3-second skate trick records 720 frames and lasts 24 seconds on screen. For natural blur shoot at 1/480 s, or faster to freeze the action.
60 fps in a 25 fps project
Conforming 60 fps to 25 fps slows it 2.4×, to 41.67% speed — a gentle, dreamy slow motion. Twenty seconds of action stretches to 48 seconds.
Phone super slow-mo at 960 fps
960 ÷ 30 = 32× slower, about 3.1% speed. Half a second of a water splash becomes 16 seconds of footage from 480 frames, and each frame can be exposed for at most about 1 ms.
Frequently asked questions
How do I calculate slow motion speed?+
Divide the capture frame rate by the playback frame rate. Footage shot at 120 fps and played at 24 fps runs 5× slower (20% speed); at 30 fps playback it runs 4× slower (25% speed).
What frame rate do I need for slow motion?+
For gentle slow motion on a 24 or 25 fps timeline, 50–60 fps (about 2–2.5×) works well. 120 fps gives 4–5× slow motion for sports and action, and 240 fps or more (8–10×) is needed for splashes, explosions and fast athletes.
What shutter speed should I use for slow motion?+
The 180° rule sets the shutter to 1 ÷ (2 × frame rate): 1/120 s at 60 fps, 1/240 s at 120 fps and 1/480 s at 240 fps. Faster shutters give crisper frames for analysing motion; you may need more light or a wider aperture.
Is 60 fps slowed to 30 fps true slow motion?+
Yes — conforming 60 fps to 30 fps shows every captured frame at half speed, a 2× slow motion with no repeated or blended frames. Slowing normal 30 fps footage to 50% instead duplicates or interpolates frames, which looks less smooth.
Why does my camera crop in high frame rate modes?+
Reading the sensor 120 or 240 times per second produces a huge amount of data, so many cameras read only part of the sensor or bin pixels, reducing resolution or adding a crop. Check your camera’s specifications for the resolution available at each frame rate.