Frame Rate & Slow Motion Calculator
Shoot at 120, play at 24, get five times the runtime.
Work out Frame Rate & Slow Motion. Shoot at 120, play at 24, get five times the runtime. Free, with no account and nothing to install.
Length on the timeline
50 s
Slow motion at 20% speed
Conforming high-speed footage to a lower timeline rate is what slow motion is. Shoot 120 and play 24 and every second of capture becomes five seconds of screen time at a fifth of the speed, with no frames invented and nothing to interpolate. The shutter speed row follows the 180-degree rule: set the denominator to twice the capture frame rate and each frame carries about half a frame of motion blur, which is what reads as natural film movement. Much faster and motion strobes; much slower and it smears. The cost is light. Shooting 120 fps at 1/240 gives each frame a fifth of the exposure that 24 fps at 1/48 would, so high-speed work needs considerably more light than the frame rate alone suggests.
How the Frame Rate & Slow Motion Calculator works
Conform high-speed footage to a timeline rate and see the playback length, the speed factor and the shutter speed that keeps motion blur natural. No frames are invented — the slow motion comes from frames you already captured.
Also known as: slow motion calculator · how slow is 120fps at 24fps · what shutter speed for 60fps · timelapse playback length
Frequently asked questions
What frame rate do I need for slow motion?
Multiply your timeline rate by how slow you want it. For half speed on a 24fps timeline, shoot 48; for 20% speed, shoot 120. Anything beyond that is a question of what your camera will do at full resolution.
What is the 180-degree shutter rule?
Set the shutter speed denominator to twice the capture frame rate — 1/48 at 24fps, 1/240 at 120fps. Each frame then carries about half a frame of motion blur, which is what reads as natural film movement rather than strobing.
Why does high-speed footage look dark?
Because the 180-degree rule forces a faster shutter. Shooting 120fps at 1/240 gives each frame a fifth of the exposure that 24fps at 1/48 would, so high-speed work needs far more light than the frame rate alone suggests.
Can I slow footage down in editing instead?
You can, but below about 50% it either stutters or relies on interpolation that invents frames. Interpolation has improved a great deal and still fails on fast motion, occlusion and anything with fine detail crossing an edge.
Should I shoot 24, 25 or 30fps?
Match the delivery. 24 for film convention, 25 in PAL regions to avoid flicker under 50 Hz lighting, 30 for North American broadcast and most online video. Mixing rates on one timeline creates judder that no amount of grading hides.
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