Shutter Speed Calculator
Enter your aperture, ISO, and lighting condition to get the correct shutter speed instantly. The calculator also finds equivalent exposures that give the same brightness with a different aperture or ISO, solves the 500 rule for star-trail-free astrophotography, and lets you work in either direction: fix the shutter speed and solve for ISO instead. The EV reference table covers everything from a moonless starfield to bright snow in full sun.
What is shutter speed?
Shutter speed is the length of time the camera sensor is exposed to light, measured in seconds or fractions of a second. A speed of 1/250 s exposes the sensor for one two-hundred-and-fiftieth of a second; 2 s holds it open for two full seconds. Together with aperture and ISO sensitivity, it forms the exposure triangle that determines how bright a photograph will be. Fast shutter speeds freeze motion; slow ones let light blur across the frame, capturing silky water, light trails, and star fields.
The exposure formula and how the calculator uses it
The core relationship is: shutter speed (in seconds) = aperture^2 / (2^EV x (ISO / 100)). The Exposure Value (EV) is a single number that describes scene brightness on a logarithmic scale: EV 15 is a bright sunny day, EV 0 is a room lit only by moonlight, and each whole step doubles or halves the light. Given any three of the four variables (EV, aperture, ISO, shutter speed), the fourth is determined. This calculator solves for shutter speed when you supply the other three, solves for ISO when shutter speed is fixed, and uses the separate 500 rule formula for astrophotography.
Understanding the 500 rule for astrophotography
Stars appear to drift across the sky because the Earth rotates. On a full-frame sensor, a star on the celestial equator moves roughly one pixel per second per 500 mm of effective focal length. The 500 rule states: maximum exposure (seconds) = 500 / (crop factor x focal length in mm). A 24 mm lens on a full-frame body gives 500 / 24 = about 21 seconds before stars form visible trails. The same lens on an APS-C camera (crop factor 1.5) gives 500 / 36 = about 14 seconds. The rule is conservative for low megapixel cameras and tight for high-resolution bodies; for precision, use the NPF rule that also accounts for pixel pitch and the declination of the star field.
Choosing shutter speed for creative effects
Beyond "correct" exposure, shutter speed is one of the most powerful creative controls available. Very fast speeds, above 1/1000 s, freeze water droplets mid-air, suspend birds in flight, and capture peak action in sports. Moderate speeds, around 1/60 to 1/250 s, are typical for everyday photography and portraiture where some subject or camera movement would cause blur. Slow speeds, below 1/30 s, demand a tripod but yield silky waterfalls, car-light trails, and buttery seascape textures. At exposures of several minutes, star circles and industrial-level light painting become possible. The handheld safety rule of thumb is: keep your shutter speed faster than 1 / (effective focal length in mm) to avoid camera-shake blur.
Common lighting conditions and EV values (ISO 100)
| Lighting condition | Typical EV | Example sunny-16 setting |
|---|---|---|
| Moonless starry sky | -6 | 30 s, f/2.8, ISO 6400 |
| Milky Way core visible | -4 | 25 s, f/2, ISO 3200 |
| Full moon outdoors | 1 | 4 s, f/2.8, ISO 800 |
| Candlelit room | 2 | 1/4 s, f/2.8, ISO 400 |
| Dimly lit street at night | 4 | 1/15 s, f/2.8, ISO 400 |
| Office / indoor fluorescent | 8 | 1/60 s, f/2.8, ISO 400 |
| Overcast daylight | 12 | 1/250 s, f/5.6, ISO 200 |
| Hazy sunshine | 14 | 1/500 s, f/8, ISO 100 |
| Full sun (Sunny 16) | 15 | 1/100 s, f/16, ISO 100 |
| Bright sun on snow / sand | 16 | 1/200 s, f/16, ISO 100 |
Exposure Values at ISO 100. Each +1 EV step means the scene is twice as bright. These are approximate: meter your scene for precision.
Frequently asked questions
What is Exposure Value (EV) and where do I find it?
Exposure Value is a number that combines shutter speed and aperture to describe how much light enters the camera, referenced to ISO 100. Many cameras display EV in the viewfinder; alternatively, use an incident light meter or look up your scene in the EV table above. Each whole EV is a "stop" - doubling or halving the light. EV 15 is the standard sunny-day reference (the Sunny 16 rule: f/16, ISO 100, 1/100 s).
How do I keep my shutter speed from going too slow when shooting handheld?
Follow the reciprocal rule: your shutter speed denominator should be at least equal to your effective focal length. On a full-frame camera with a 50 mm lens, stay above 1/50 s. On a 1.5x crop body with the same lens, stay above 1/75 s because the effective focal length is 75 mm. Image stabilisation (IBIS or OIS) typically buys 3-5 extra stops, so you can often shoot at 1/10 s or slower with stabilisation active.
Why does the 500 rule give a different number on a crop sensor?
Because the effective focal length is longer. A 24 mm lens on a 1.5x APS-C body captures the same field of view as a 36 mm lens on full frame. Stars appear to move at the same angular speed regardless of sensor size, but a tighter field of view means that movement crosses more pixels in a shorter time. Multiplying the crop factor into the denominator corrects for this.
What is the difference between the 500 rule and the NPF rule?
The 500 rule is simple and easy to compute mentally; the NPF (Niepce-Picard Formula) is more accurate. NPF accounts for pixel pitch (the physical size of individual sensor pixels) and the declination of the star: stars near the celestial poles drift much more slowly than those near the equator. On high-resolution bodies with small pixels, the 500 rule can be optimistic by 20-30%. If pinpoint stars matter, use an NPF calculator and input your camera model's pixel pitch.
How do I calculate an equivalent exposure?
An equivalent exposure keeps the same overall brightness but with a different combination of settings. To move to a faster shutter speed by one stop (halving the time), you must either open the aperture one stop (multiply f-stop by 0.71, e.g., f/5.6 to f/4) or double the ISO. Use the "Find ISO" mode to work out what ISO you need to use a specific shutter speed without changing aperture.
What shutter speed do I need to freeze motion?
It depends on how fast the subject is moving and how close it is. A rough guide: use 1/500 s or faster for sports and running, 1/1000 s or faster for birds in flight and fast vehicles, and 1/2000 s or faster to freeze water droplets or extreme sports. For slow-moving subjects such as people walking, 1/125 s is usually sufficient.