Slow Motion Calculator

Tell me the fps you shoot at and the timeline you edit in — I'll tell you how much it slows down, how long it runs on screen and what shutter you need.

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Your slow motion

Timeline FPS
Playback duration
0s
0slow-motion factor
0playback speed
0suggested 180° shutter
0frames captured

For natural motion, keep the 180° rule: shutter ≈ 1/(2 × capture fps).

Quick scenarios

How slow motion is calculated

The idea is simple: you record more frames per second than you play back, and playing them at normal speed stretches the action. The factor is just a division:

factor=capture fps ÷ timeline fps

Everything else follows: screen duration is the real duration times that factor, and playback speed is its inverse as a percentage (100 ÷ factor). For natural motion blur, the 180° rule asks for a shutter of roughly 1/(2 × capture fps).

If the factor comes out below 1, you are not slowing anything down: you are speeding it up. The clip will run shorter than the real action.

Example: 120 fps edited at 24p

You record 3 seconds of a splash at 120 fps and edit on a 24 fps timeline:

  • Factor = 120 ÷ 24 = 5×.
  • Screen duration = 3 × 5 = 15 seconds.
  • Playback speed = 100 ÷ 5 = 20 %.
  • Frames captured = 3 × 120 = 360.
  • 180° shutter = 1/(2 × 120) = 1/240.

That 1/240 is what explains the usual "I don't have enough light" complaint: compared with a normal 1/50 at 24 fps you have lost more than two stops, and you have to win them back with aperture, ISO or more light.

Slow motion FAQ

How is the slow-motion factor calculated?
Divide your capture fps by your timeline fps. Shoot at 120 fps and edit at 24 and the factor is 5×: the action lasts five times longer on screen and plays back at 20 % of its real speed.
How many fps do I need for good slow motion?
It depends how much you want to slow things down. For a subtle effect, double your timeline is enough (60 fps to edit at 30). For clearly cinematic slow motion, 4× or 5× (96-120 fps over 24). Above 240 fps you are in high-speed territory, with resolution crops and a lot of light required.
What shutter should I use when shooting high frame rates?
The 180° rule says shutter should be roughly 1/(2 × capture fps): at 120 fps, 1/240. Keeping it gives natural motion blur. Push the shutter much faster and every frame is frozen, so the slowed-down result looks stuttery instead of fluid.
Why do I need so much light to shoot at 120 fps?
Because the shutter has to be far quicker. Going from 1/50 (at 24 fps) to 1/240 (at 120 fps) costs more than two stops of light, and you have to make them back by opening the aperture, raising ISO or adding light.
Can I slow footage down in post instead of shooting more fps?
You can, but it is not the same. If you shot at 24 fps and halve the speed, the software has to invent the missing frames (interpolation) or repeat them, and it usually shows. Shooting at a higher frame rate captures real information, which is why the result is clean.
What if my capture fps is lower than my timeline fps?
Then it is not slow motion but a speed-up: the factor drops below 1 and the clip plays faster and shorter than the real action. The calculator detects this and labels it as sped up rather than slow motion.