Slow-motion calculator: speed % for 60, 120 and 240 fps footage

How to work out your slow-motion speed

1. Set Recorded at (fps) to the frame rate of your clip, for example 120. Pick a preset or type a custom value.
2. Set Timeline frame rate (fps) to your sequence or project frame rate, for example 24.
3. If you want the new length, type the Clip length as recorded in seconds or mm:ss.
4. Read the results. Slowest smooth speed is the percentage to type into your editor, Slow-down factor shows how many times slower that is, and New clip length shows how long the clip will run.
5. To try another speed, enter it in Check a speed to see whether every frame is still unique or frames will repeat.

The formula

Slowest smooth speed = timeline frame rate ÷ recorded frame rate × 100. At that speed every recorded frame is shown exactly once.

NTSC rates trip people up. 59.94 and 23.976 are exact fractions (60000/1001 and 24000/1001), so 59.94 fps on a 23.976 timeline is exactly 40%. Mixed pairs aren't round: 60 fps on 23.976 is 39.96%, and 59.94 fps on 24 is 40.04%. The calculator uses the exact fractions.

Speeds above and below that number

Below the smooth speed, for example 30% for 60 fps on a 24 fps timeline, there aren't enough recorded frames. The editor repeats frames, which stutters, or creates new ones with frame blending or optical flow, which can smear or warp fast motion. Above it, every frame shown is real but some are skipped. Unless the speed is an exact multiple of the smooth speed, the skips fall unevenly, which can show as a slight judder.

Set the speed in your editor

You can tell the editor to play the clip at the timeline's frame rate (interpret or conform it), which gives the slowest smooth speed directly. Or type the calculator's percentage into a speed control. These steps come from each editor's own documentation, checked in October 2026. Adobe's help pages couldn't be opened by our tools, so the Premiere Pro and After Effects steps follow those pages as indexed by search engines. Menus can move between versions.

Premiere Pro

• Interpret Footage: select the clip in the Project panel, choose Modify > Interpret Footage, pick "Assume this frame rate" and enter your timeline frame rate. This changes every use of that clip in the project, and Adobe notes that the audio changes along with the video.
• Speed/Duration: select the clip in the timeline, choose Clip > Speed/Duration and enter the percentage in Speed. Below the smooth speed, set Time Interpolation to Frame Blending or Optical Flow. Frame Sampling repeats or drops frames.

After Effects

• Conform To Frame Rate: select the footage in the Project panel, choose File > Interpret Footage > Main, select Conform To Frame Rate and enter your composition's frame rate. Adobe notes that this changes the video's duration but not the audio, so sound won't line up with the slowed picture.
• Time Stretch: Layer > Time > Time Stretch works in duration, the inverse of speed. A Stretch Factor of 250% (slow-down factor × 100) is 40% speed.

DaVinci Resolve

• Clip Attributes: in the Media Pool, right-click the clip, choose Clip Attributes, open the Video panel and set Video Frame Rate to your timeline frame rate. Blackmagic's manual says this changes the clip's duration and playback speed, and that its audio is unaffected.
• Change Clip Speed: right-click the clip in the timeline, choose Change Clip Speed and enter the percentage. Below the smooth speed, set Retime Process to Frame Blend or Optical Flow. It is in the Inspector under Retime and Scaling, or for the whole project in Project Settings > Master Settings > Frame Interpolation. Nearest duplicates frames.

Final Cut Pro

• Automatic Speed: select the clip in the timeline, click the Retime pop-up menu below the viewer and choose Automatic Speed. Apple's example is a 120 fps clip in a 30 fps project, which then plays every original frame at 30 fps.
• Custom speed: choose Custom from the Retime pop-up menu, select Rate and enter the percentage. Below the smooth speed, choose Video Quality from the same menu and pick Good (Frame Blending), Better (Optical Flow) or Best (Machine Learning). Apple says the machine-learning option needs a Mac with Apple silicon.

CapCut

CapCut's own guide (desktop app) says to select the clip, open Speed, keep Normal selected and drag the speed bar left from 1. The bar works as a multiplier, so 40% is 0.4. Its Smooth slo-mo option smooths the result. The frame rate you export at is the timeline frame rate to enter above. We found no CapCut documentation on how it handles high-frame-rate clips, so play back the export to check.

Limits

• Slowing past the smooth speed, for example 30 fps footage at 10%, needs frame blending or optical flow, and the result won't look like footage shot at a high frame rate.
• It trusts the frame rates you enter. Check the frame rate your editor reports for the file, especially for phone slow-motion clips and screen recordings, which may not match the camera setting or may vary during the clip.