Two multiplications, and one of them hurts
The whole calculation is this. Frames equal shooting duration divided by interval. Clip length equals frames divided by playback frame rate. Put them together and the shooting time needed for a clip of a given length is clip length × frame rate × interval.
That last expression is where the pain lives, because two of its three terms are small numbers that multiply into a large one. Twenty seconds of clip, at 24 fps, at a 10 second interval, is 480 frames and 80 minutes of shooting. Nobody budgets 80 minutes for 20 seconds of screen time until they have done it once. The reverse mode on this calculator exists specifically so the discovery happens during planning rather than in the field.
The speed-up factor is the other useful framing: interval × frame rate tells you how much faster than reality the clip runs. A 5 second interval at 24 fps is 120x, so one hour of the world becomes 30 seconds of clip. If you think in terms of how fast the sun should appear to cross the frame, this is the number to reach for.
Choosing the interval by what is moving
Interval is a creative decision disguised as a technical one. Too short and the finished clip barely accelerates anything, and you have shot thousands of frames for nothing. Too long and the motion stops being motion and becomes a stutter.
| Subject | Typical interval | Why |
|---|---|---|
| People and traffic close by | 1–2 s | Fast subjects need dense sampling or they jump |
| Fast clouds, crowd flow | 2–4 s | Enough sampling to keep the motion continuous |
| Slow clouds, shadows moving | 5–10 s | Nothing moves far between frames anyway |
| Sunset and sunrise | 3–6 s | Light changes faster than the geometry does |
| Stars | 15–30 s | The exposure itself is that long |
| Construction, plants, decay | Minutes to hours | The change is what you are showing, not the movement |
The rule underneath the table is that the subject should not move more than a small fraction of the frame between consecutive frames. A cloud crossing the frame in two minutes wants an interval that gives you well over a hundred frames of that crossing. Anything less and the eye reads jumps.
Card space, battery and the write window
Frame count times file size is the storage, and raw timelapse eats cards at a rate that surprises people who normally shoot video. A three hour sunset at a 4 second interval is 2,700 frames; at 25 MB each that is 67.5 GB, for a clip under two minutes long. The shoot storage calculator handles the offload and copies side of that, and the arithmetic there is the same arithmetic.
The interval must also be long enough to actually take the picture. Exposure time, raw write time, in-camera noise reduction if it is switched on, and the mechanical reset all happen inside the interval. Long-exposure noise reduction is the usual saboteur: it doubles the effective time per frame silently, and a sequence that seemed to have margin starts dropping frames irregularly. Test a few minutes of the sequence and count the files before committing to a long run.
The things the arithmetic does not cover
Flicker is the main one. Aperture blades do not close to precisely the same place each time on many lenses, so a sequence shot in aperture priority with a small aperture can pulse frame to frame. The usual field fixes are to shoot in full manual, or to use the lens-detach trick so the aperture stays fixed, and then to run a deflicker pass in post. None of it shows up in a frame count.
Then there is everything about the location. Long runs mean a tripod standing in one place for hours, which is a different proposition on a sidewalk than in your own yard. Filming permits, tripod rules, drone regulations and private property permissions all exist, and they vary by jurisdiction and by landowner rather than following one national rule. Confirm before the shoot rather than after someone asks what you are doing. And if the run spans a big change in light, plan the exposure ramp before you start — the shot that begins at f/8 in daylight and ends under stars is a different technical exercise from one that stays in the same light the whole time.
Questions people ask
How long do I have to shoot for ten seconds of timelapse?
Clip length × frame rate × interval. At 24 fps that is 240 frames; at a 2 second interval it is 8 minutes, at 5 seconds it is 20 minutes, at 10 seconds it is 40 minutes, and at a 30 second interval it is two hours. The frame rate matters as much as the interval and gets forgotten — switching a delivery from 24 to 60 fps multiplies the required shooting time by two and a half for the same clip length. Decide the delivery frame rate before you decide the interval.
Should I shoot stills or shoot video and speed it up?
Below roughly a two second interval, video and a speed ramp in the edit is often the better trade: no shutter wear, no interval arithmetic, and smoother motion, at the cost of resolution, dynamic range and the ability to pull a still from it. Above that, stills win clearly, because video would mean recording and discarding enormous amounts of footage. The other reason to shoot stills is any run where the exposure has to change during the sequence, since a raw frame gives you room to correct that afterwards which a compressed video frame does not.
How many frames per second should the finished clip be?
Match the project it lands in. If the rest of the edit is 24 fps, deliver 24 or the cut will stutter at the joins. The lower the frame rate, the fewer frames you have to shoot for the same clip length, which is a genuine practical argument for 24 or 25 over 60 when the choice is open. Some people shoot at a higher frame rate deliberately so there is room to slow the clip down later, which is a valid plan as long as the extra shooting time was budgeted for.
What causes timelapse flicker and can I calculate it away?
No calculation touches it. Flicker comes from small frame-to-frame variations in exposure, most commonly from an aperture that does not stop down to exactly the same position on every actuation, from automatic exposure modes making small corrections, or from artificial lighting cycling with mains frequency. The fixes are procedural: full manual exposure, a fixed aperture, avoiding auto white balance, and a deflicker pass in post. Test a short sequence and look at it at speed before committing hours.
How much card space does a long timelapse need?
Frames × file size, and the frame count is usually larger than expected. Six hours at a 4 second interval is 5,400 frames; at 30 MB per raw frame that is 162 GB, which is more than one card on many setups. Work out the number before the shoot rather than swapping cards in the dark, and remember that swapping a card mid-sequence puts a gap in the run unless the camera can do it without stopping the intervalometer.