Plan your time-lapse

What a time-lapse needs

A time-lapse is a set of still photos, each taken after a fixed wait, played back at a normal video speed. Everything about planning one comes down to three numbers that are tied together: the real length of what you are filming, the gap between photos, and the length of the finished clip. Fix any two and the third follows. The calculator has a mode for each. It also tells you the number of frames, the speed-up of the finished clip, and, if you give it the file size, the space the frames will take.

The formulas

Frames = clip length in seconds × frames per second. Interval = real length of the event ÷ frames. Clip length = frames ÷ frames per second, where frames = event length ÷ interval, rounded down. Shooting time = frames × interval. Speed-up = event length ÷ clip length. Storage in gigabytes = frames × file size in megabytes ÷ 1,000. Batteries = frames ÷ shots per battery, rounded up. Because a camera has to finish the exposure and write the file before the next frame, the interval must be longer than the exposure time, and the calculator warns you when it is not.

A worked example

A 2-hour sunset turned into a 10-second clip at 30 fps needs 10 × 30 = 300 frames, so the interval is 7,200 s ÷ 300 = 24 seconds, and the clip plays 720× faster than real life. With 25 MB frames that is 7.5 GB, and a 64 GB card holds 2,560 frames, enough for 17.1 hours at this interval. A 4-hour event shot every 5 seconds gives 2880 frames, a 120-second clip at 24 fps. In the other direction, a 10-second clip at 24 fps with a 10-second interval means shooting 240 frames, which takes 40 minutes.

Limits and mistakes

Choosing the interval by feel. Fast subjects such as clouds and traffic want short intervals (a few seconds); slow ones such as shadows, construction or a blooming flower want long ones. Too long an interval makes the motion jump. If you are unsure, shoot more frames than you need and drop some while editing, but you cannot add frames you did not take.

Exposure and interval are linked. Each frame needs its exposure to finish before the next starts. For a day-to-night scene the exposure gets longer as the light fades, so keep the interval above the longest exposure. See the exposure value calculator for equivalent settings and the depth of field calculator for focus.

The NPF exposure is a starting point. The formula for the longest exposure before stars trail, T = (35 × N + 30 × P) ÷ F, is credited to Frédéric Michaud of the Société Astronomique du Havre. We checked it against two secondary sources, an article by Nando Harmsen on Fstoppers (August 10, 2020), whose worked example for a full-frame camera with a 16 mm f/2.8 lens we reproduce (16.2 s), and a calculator page; we could not find Michaud’s original text. One commenter on that article disputes whether aperture and pixel pitch should matter at all. Take the answer as a first guess, then look at a test frame at 100%.

Memory and power. The file size and the shots per battery come from your own camera, so the calculator does not guess them. Test with a short run before an important shoot, and add a margin.

Common questions

How do I calculate the interval for a time-lapse?

Divide the real length of the event by the number of frames in the finished clip. The clip’s frames are its length in seconds times the frame rate. For a 2 hours sunset made into a 10-second clip at 30 fps you need 300 frames, so the interval is 7,200 ÷ 300 = 24 seconds.

How many frames do I need for a time-lapse video?

Clip length in seconds times frames per second: 10 seconds at 24 fps is 240 frames, at 30 fps 300, at 60 fps 600. Many people shoot a bit more than needed so there is room to trim and to ease the speed at the ends.

Which frame rate should I choose: 24, 25, 30 or 60?

Match your project. 24 fps is the standard for film-style work, 25 fps for PAL video in Europe and much of the world, 30 fps (nominally) for NTSC video in the US, and 60 fps for smoother motion or slow-motion stretches. A higher rate needs more frames for the same clip length: for a 10-second clip it is 240, 250, 300 or 600 frames.

How long will the shoot take?

Frames times interval. A 10-second clip at 24 fps with a frame every 10 seconds takes 240 frames, which is 40 minutes of shooting. In the other direction, 4 hours at one frame every 5 seconds gives 2880 frames, a 120-second clip at 24 fps.

How much memory card space do I need?

Frames times the file size of one frame. The file size depends on your camera and format, so type your own: with 25 MB frames (an example, a mid-size raw file) the 300-frame plan needs 7.5 GB, and a 64 GB card holds 2,560 such frames. Long shoots add up: always carry a card with room to spare.

What is the NPF rule for night-sky time-lapses?

It is a formula for the longest exposure before stars start to blur into trails, attributed to astrophotographer Frédéric Michaud of the Société Astronomique du Havre: T = (35 × N + 30 × P) ÷ F, with T in seconds, N the aperture f-number, P the pixel pitch in micrometers and F the focal length in millimeters. For a full-frame camera with a 36 mm sensor 6,720 pixels wide the pitch is 5.36 µm, so a 16 mm lens at f/2.8 gives (98 + 160.7) ÷ 16 = 16.2 seconds. It is a starting point; check frames at full size, since it does not consider where in the sky you aim.

Related: the exposure value calculator, the depth of field calculator, the aspect ratio calculator for the frame shape and the download time calculator for moving files.

Planning arithmetic only; check your camera’s manual for its minimum interval, buffer and battery behavior. Sources, read October 27, 2026: the frame, interval and storage formulas are arithmetic on the definitions of frame rate and file size; NPF rule: Nando Harmsen, “Using the NPF Rule for Photographing Night Skies,” Fstoppers, August 10, 2020 (formula and worked example, credited to Frédéric Michaud of the Société Astronomique du Havre), cross-checked against Imagen AI’s NPF calculator page; original publication not located. How we check our calculators.