Time-lapse interval calculator: how often to take a photo
The short answer takes two sums. First work out how many photos you need, then spread them over the time you’re filming:
- Photos needed = length of the finished video in seconds × frame rate
- Interval = how long the event lasts ÷ photos needed
So a two-hour sunset that should play for 20 seconds at 25 frames per second needs 20 × 25 = 500 photos, one every 7,200 ÷ 500 = 14.4 seconds. The calculator below does the sums for you, and adds how many photos that is per day and how much space they’ll take.
Time-lapse interval calculator
How to choose an interval
The calculator starts from how long you want the video to be. The other way to think about it is how fast you want things to move on screen. Every second of video shows interval × frame rate of real time. At one photo every 2 seconds and 25 frames per second, each second of video covers 50 seconds: clouds race, but people still walk across the frame in a few jumpy steps. At one photo every 10 minutes, each second covers more than four hours and the sun sweeps across the sky in two to four seconds, depending on the season.
Two rules of thumb pull in opposite directions:
- Shorter intervals look smoother. If something moves a long way between frames, it jumps rather than glides. Pick an interval short enough that the fastest thing you care about only moves a little between photos.
- Longer intervals cost less. Fewer photos means less storage, less wear on the camera and less to sort through. And with very slow subjects, a short interval just gives you hours of film where nothing seems to happen.
Which frame rate? 24 frames per second became the standard for sound film, and television grew up at 25 frames per second in countries with 50 Hz mains, including the UK and most of Europe, and 30 (strictly 29.97) in countries with 60 Hz. Any of them works for a time-lapse; 25 is a safe choice in the UK. 60 frames per second looks silkier but needs more than twice as many photos as 25 for the same length of video.
Typical intervals by subject
These are rules of thumb, not laws. They’re the kind of starting points photographers share, and the right answer depends on how fast your subject moves, how close you are, and how long you want the film to be. Do a short test run if you can.
| Subject | Starting interval | Why |
|---|---|---|
| Fast clouds, traffic, crowds | 1 to 2 seconds | Cars and people cross the frame in seconds. Longer gaps turn them into flashes. |
| Slow clouds, sunsets and sunrises | 2 to 10 seconds | The light changes over an hour or two. A few seconds keeps the clouds flowing and gives a usable clip from one evening. |
| Shadows moving, a day in a city | 15 to 60 seconds | Shadows creep slowly; a whole day still fits into a short clip. |
| Tides | 30 seconds to 1 minute | On most coasts, including the UK's, around six hours from high to low water, so one photo a minute turns each tide into about 15 seconds. |
| Plants growing, flowers opening | 5 to 30 minutes | Seedlings and flowers move over hours and days. Shorter gaps catch fast movers, such as a bean sprouting. |
| A building going up | A few photos a day, in daylight | Months of work have to fit into a minute or two, so you keep only one to a few frames a day. Shoot more and keep the best (see below). |
| Seasons over a year | One photo a day | 365 frames is about 15 seconds at 25 frames per second, enough to see a year turn. |
| Glaciers, coastlines, reforestation | One photo a day, or fewer | Change is measured over years. A daily frame lets you choose good-weather days later. |
How many photos do you need for a time-lapse?
A few worked examples, all at 25 frames per second:
- An hour of sunset at one photo every 3 seconds is 1,200 photos, which plays for 48 seconds. Trim it, or use a longer interval if you want a shorter clip.
- Seedlings over five days, as a 20-second clip, need 500 photos, one about every 14 minutes. Unless you light them at night, half of those will be dark, so either shoot twice as often in daylight or add a grow light.
- A year-long build as a one-minute film needs 1,500 photos, about four a day. At 5 MB each that’s only 7.5 GB. If you shoot only in working hours, spread those four across the working day.
Long projects: the interval isn’t the whole story
For a time-lapse that runs for weeks or months, the calculator will tell you that you need only a handful of photos a day. Taking exactly that many, on a fixed timer, is the classic way to end up with a flickering film: sunny at noon one day, grey the next. Why long-term time-lapses flicker goes through the causes.
The better approach is to separate two numbers: how many photos you keep each day, which is what the calculator works out, and how many you take. Take many candidates in each period, then keep the one that best matches its neighbours. Photographers do this by over-shooting, for example one photo every ten minutes, and choosing by hand later, which costs storage and time. We compare it with deflicker software in Over-shoot, deflicker or select?
SmoothLapse was built to make that choice on the camera itself: a Raspberry Pi takes photos continuously, compares each with the one it kept for the previous period, and keeps only the closest matches. It isn’t available at the moment. The 2021 version doesn’t run on today’s Raspberry Pi OS, and we’re rebuilding it. If you’re planning a long project, you can join the early-access list at the bottom of this page.
Storage and power
The calculator’s storage figure is the floor. Over-shooting multiplies it, and a camera running for months needs somewhere safer than an SD card to put the photos, plus reliable power. The Raspberry Pi time-lapse checklist covers storage, power and weatherproofing.
Setting the interval on a Raspberry Pi
On current Raspberry Pi OS the camera tool is rpicam-still (called libcamera-still on older releases). It has a built-in time-lapse mode: --timelapse sets the gap between photos in milliseconds, and --timeout sets how long to keep going. A timeout of 0 runs until you stop it. This takes a photo every 14.4 seconds for two hours (-n turns off the preview window):
rpicam-still -n --timeout 7200000 --timelapse 14400 -o frame%05d.jpg The %05d numbers the files frame00000.jpg, frame00001.jpg and so on, which is the order most video tools expect. The timeout can also take a unit, so --timeout 120min means the same as --timeout 7200000. For long gaps, such as a few photos a day, there's a simpler route, which the Raspberry Pi documentation also shows: a small script that takes one photo, named with the date and time, run on a schedule by cron.
The short version: photos needed = video seconds × frame rate, and interval = event length ÷ photos needed. Use 1 to 10 seconds for clouds, traffic and sunsets, minutes for plants, and a few frames a day for builds and seasons. For long projects, take many more photos than you need and keep the best.
Sources: Raspberry Pi camera software documentation (rpicam-still, --timelapse, --timeout and the cron example); Wikipedia, Frame rate (24 frames per second for sound film, and 29.97) and PAL (25 and 30 frames per second, and 50 and 60 Hz mains).