Timecode & Frame Rate Lab

Timecode calculator: the math, honestly explained

A timecode calculator converts between three ways of naming the same moment: frames (an integer count), timecode (HH:MM:SS:FF in SMPTE format), and seconds (wall-clock duration). The bridge is the frame rate — and for NTSC rates the frame rate is a fraction, not a round number: 29.97 fps is really 30000/1001, 23.976 is 24000/1001. This lab does every conversion with exact fractional math, so errors never accumulate.

Adding and subtracting timecode

Timecode addition works by converting each timecode to a frame count, adding the integers, and converting back. Example at 24 fps: 01:00:00:00 + 00:00:10:12 = 01:00:10:12 (252 frames added). This is the core of the timecode duration calculator workflow in Premiere Pro, Avid and DaVinci Resolve — summing shot durations, or subtracting an in-point from an out-point.

Frames to seconds and back

The frames to seconds calculator question ("how long is 150 frames?") is just division: frames ÷ fps. 150 frames at 25 fps = 6 seconds = 00:00:06:00. After Effects and Blender users do this constantly when converting frame ranges to durations.

Frame rate conversion

A frame rate converter for calculators (not file converters) answers: "my timeline is 10 seconds at 24 fps (240 frames) — how many frames is that at 30 fps?" Answer: 300 frames, 00:00:10:00. Special cases: 24 fps to 25 fps conversion is a 4.17% speedup (the PAL legacy); 23.976 vs 24 fps differ by 0.1% — a full day of 23.976 footage is 86.4 seconds shorter than the 24 fps clock claims.

Slow motion

Slow motion math is one division: shoot fps ÷ playback fps = slow factor. 120 fps shot played back at 24 fps = 5× slow — 10 seconds of recording becomes 50 seconds on screen. 60 fps over 24 fps = 2.5×; 240 fps over 24 fps = 10×. That is the whole slow motion frame rate calculator: no magic, just the ratio.

Drop frame vs non-drop frame

At 29.97 fps, a non-drop-frame clock lags ~3.6 seconds per hour behind real time. Drop-frame timecode fixes this by skipping frame numbers :00 and :01 at the start of every minute except every 10th — no frames are lost, only numbers. So 29.97 drop frame timecode 01:00:00:00 really is one hour: 107,892 frames.

How this lab beats single-purpose converters

Most "timecode calculator" pages do one conversion. Search results for "frame rate converter" are polluted with file-conversion software (upload a video, convert the file) — not calculators at all. This lab is the calculator suite the intent actually asks for: five modes, exact NTSC fractional math, drop-frame done per SMPTE 12M, all offline in your browser.

Quick answers to common searches

Timecode addition calculator

Add two SMPTE timecodes by converting each to frames, summing, and converting back. Try 01:00:00:00 + 00:00:10:12 at 24 fps in the Timecode Arithmetic tab → 01:00:10:12.

Drop frame timecode calculator

Use the Drop-Frame Lab tab: pick 29.97 or 59.94 fps, enter a duration, and compare exact frame counts for drop-frame vs non-drop-frame, including how many frame numbers are dropped per hour.

Timecode to frames

Multiply out the timecode at the nominal rate, then subtract dropped frame numbers for DF. The Frames ↔ TC ↔ Sec tab converts either direction instantly.

30fps to 60fps converter

Duration-preserving: 10 s at 30 fps = 300 frames = 600 frames at 60 fps = 00:00:10:00. One-click preset in the FPS Converter tab.

24fps to 25fps converter

A 4.17% speedup (PAL legacy): 100 s at 24 fps plays in 96 s at 25 fps. One-click preset in the FPS Converter tab.

NTSC PAL converter

NTSC rates (23.976, 29.97, 59.94) use fractional frame rates; PAL rates (25, 50) are whole. The FPS Converter tab handles every NTSC↔PAL pair with exact math.

120fps slow motion

120 fps played back at 24 fps = 5× slow motion. At 30 fps playback it is 4×. Enter any shoot/playback pair in the Slow-Mo Planner.

Is 60fps slow motion?

Only when played back slower than 60 fps — at 24 fps it is 2.5× slow motion. Slow motion is the ratio of shoot fps to playback fps, not the shoot rate alone.

What frame rate for slow motion?

For 2× slow motion at 24 fps delivery, shoot 48–50 fps; for 5×, shoot 120 fps; for 10×, shoot 240 fps. See the combo table in the Slow-Mo Planner.

Timecode calculator Premiere

Copy in/out timecodes from Premiere Pro's monitors into the Timecode Arithmetic tab (Subtract) with the matching frame rate — this is the standard timecode duration calculator workflow.

Frames to seconds calculator After Effects

Frames ÷ fps = seconds. 150 frames at 25 fps = 6 s. The triple converter tab does this for every supported frame rate with exact NTSC fractions.

Frequently asked questions