How to Calculate a Time-Lapse Interval

How often should the camera fire during a two-hour sunset? The answer is one photo every 10 seconds, when you want a 30-second clip at 24 frames per second. One short division gets you there.

This guide shows how to work backward from the clip you want to the gap between photos. You will also learn how many frames you need, how much card space they take, and how shutter speed fits inside the interval.

The Time-Lapse Interval Formula

A time-lapse is a video built from still photos taken at a set gap. That gap is the interval. You play the photos back at a normal video frame rate, so slow events race across the screen.

The math has three parts: how long the event lasts, how long the clip should run, and the playback frame rate. Put them together and the interval falls out:

Interval = event duration / (clip length x fps)

The bottom half of that fraction is simply the number of frames you need. A 30-second clip at 24 fps needs 30 x 24, or 720 frames. Spread 720 frames across 7,200 seconds of sunset, and you get one frame every 10 seconds.

Keep every time in the same unit. Event length is usually given in hours or minutes, but the interval is in seconds. Our guide to converting seconds, minutes and hours covers those unit swaps. Two hours is 7,200 seconds, and 45 minutes is 2,700 seconds.

How Do You Plan an Interval for a Real Shoot?

Start from the clip you want to show, not from the camera. Then work back to the gap between photos with five short moves.

1. Time the event. Estimate how long the change lasts. A sunset glow might run 2 hours, which is 7,200 seconds.
2. Pick the clip length. Decide how long the finished video should play. Here we choose 30 seconds.
3. Choose the frame rate. Our calculator offers 24, 25, 30 and 60 fps. We pick 24 fps for a film look.
4. Count the frames. Multiply clip length by frame rate. 30 x 24 gives 720 frames.
5. Divide for the interval. Split the event seconds by the frames. 7,200 / 720 gives a 10-second interval.

The result also tells you the speed-up. Multiply the interval by the frame rate. A 10-second gap played at 24 fps runs 240 times faster than real life.

Wikipedia gives a simple case of this rule. Frames shot at 1 per second and played at 30 fps look 30 times faster. The same logic scales to any interval you pick.

Round the interval down when it lands between settings. A shorter gap gives a few extra frames, and extra frames can be trimmed in editing.

How Many Frames and How Much Card Space?

Frames equal shoot seconds divided by the interval, and storage equals frames times file size. These two numbers decide whether one memory card and one battery will last.

Take the example from our calculator page. A 60-minute sunset shot every 3 seconds gives 3,600 / 3, or 1,200 frames. At 30 fps, those frames play for 40 seconds.

Our calculator uses about 25 MB for a RAW file and 5 MB for a JPEG. So 1,200 RAW frames fill about 30,000 MB, or 30 GB. The same shoot in JPEG needs about 6 GB.

Double the interval to 6 seconds, and the frames drop to 600. The clip shrinks to 20 seconds, and the card space halves to about 15 GB in RAW.

RMCAD suggests shooting more frames than you need. The extra frames give you room to trim the start and end in editing. They also help when a person walks through the frame.

Our calculator counts frames and space only. It does not know your exact file size or the time the camera needs to write each file.

Should the Shutter Stay Open Longer Between Frames?

Often, yes. For smooth motion, Wikipedia describes setting the exposure to about half the frame interval. A 30-second interval then pairs with a 15-second exposure.

Shutter speed and interval are two different clocks. The shutter speed is how long each photo gathers light. The interval is the gap from the start of one photo to the start of the next.

Video shooters use the same idea. The Tufts University Library guide says shutter speed should be about double the frame rate. At 24 fps, that means about 1/50 of a second, the closest camera setting to 1/48.

A time-lapse stretches that rule across seconds. Wikipedia calls a quick 1/50-second exposure every 30 seconds a “stop-motion” look. Clouds and cars jump from frame to frame instead of flowing.

Long exposures in daylight need less light reaching the sensor. That brings in aperture, ISO and filters, which our guide to the exposure triangle explains in full.

The exposure must also end before the next frame starts. A 5-second exposure fits a 10-second gap. A 12-second exposure does not fit at all.

Interval Errors and Better Choices

Interval plans tend to go wrong in a few simple ways, from mixed units to starting at the wrong end. The table below pairs six of them with a better habit.

Here is one more check with a night sky. Our calculator has a preset of 240 minutes at a 20-second interval. That gives 14,400 / 20, or 720 frames, which plays for 30 seconds at 24 fps or 24 seconds at 30 fps.

RMCAD also warns that long sessions drain batteries and fill cards fast. Carry a spare battery and a large, fast card for any shoot longer than an hour.

Try it with your own plan. Enter a shoot length and a trial interval in the time-lapse frames and clip calculator to confirm the clip length before you leave home.

Time-Lapse Intervals: Frequently Asked Questions

Sources and Further Reading

This article explains time-lapse planning math for learning and hobby use. Real file sizes and camera write times vary by model. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 27, 2026.