Last updated: July 16, 2026
Shutter Speed Calculator
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Quick Answer
The Shutter Speed Calculator uses the APEX photographic exposure formula t = (100 × N²) / (S × 2^EV) to compute the correct camera exposure time. Inputs are the scene's Exposure Value (EV), aperture f-number (N), and ISO sensitivity (S). Results are expressed in seconds (e.g., 0.002 s = 1/500 s). The calculator also provides motion photography advice based on the resulting shutter speed.
To calculate shutter speed, divide 100 times the aperture squared by the ISO times 2 to the power of the Exposure Value. For example, at f/8, ISO 100, EV 15 (bright sun): shutter speed = 100 × 64 / (100 × 32768) = 1/512 second.
Key Takeaways
- Shutter speed is calculated as t = (100 × N²) / (S × 2^EV), based on the APEX photographic exposure system standardized by ANSI.
- The Exposure Value (EV) scale runs from -7 (Milky Way) to 16 (sand/snow in sunlight), with EV 15 representing typical bright sun.
- Doubling ISO or opening aperture by one stop allows you to use a shutter speed one stop faster with the same exposure.
- To avoid camera shake when hand-holding, use a shutter speed faster than 1/(focal length in mm) — the reciprocal rule.
- Long exposures (>1 s) require a tripod and remote shutter release to avoid motion blur from camera movement.
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Formula
t = (100 × N²) / (S × 2^EV)
Where:
- t=Shutter Speed(seconds)
- N=Aperture (f-number)(f/N)
- S=ISO Sensitivity(ISO)
- EV=Exposure Value(EV)
Worked Examples
Bright Sunny Day Portrait
Standard sunny day portrait at f/8, ISO 100, EV 15 (Sunny 16 rule variant)
- 1Numerator: 100 × 8² = 6400
- 2Denominator: 100 × 2^15 = 3,276,800
- 3Shutter speed = 6400 / 3,276,800 ≈ 0.00195 seconds
- 4Expressed as a fraction: 1/512 sec
Indoor Sports Action Shot
Floodlit sports arena at f/2.8, ISO 1600, EV 8
- 1Numerator: 100 × 2.8² = 784
- 2Denominator: 1600 × 2^8 = 409,600
- 3Shutter speed = 784 / 409,600 ≈ 0.00191 seconds
- 4Displayed as: 1/523 sec — fast enough to freeze most motion
Milky Way Night Photography
Dark sky astrophotography at f/2.8, ISO 3200, EV -7
- 1Numerator: 100 × 2.8² = 784
- 2Denominator: 3200 × 2^(-7) = 25
- 3Shutter speed = 784 / 25 = 31.36 seconds
- 4Use tripod and remote shutter release for this long exposure
Introduction
The Shutter Speed Calculator determines the optimal camera shutter speed based on exposure value (EV), aperture (f-number), and ISO sensitivity. Using the fundamental photographic exposure equation t = (100 × N²) / (S × 2^EV), this tool helps photographers achieve correct exposure in any lighting condition — from starlit nights to brilliant noon sunlight. This formula is based on the APEX (Additive Photographic EXposure) system standardized by ANSI.
Understanding Shutter Speed
Shutter speed (or exposure time) controls how long the camera sensor is exposed to light. Measured in seconds or fractions of a second (e.g., 1/250 s), it is one of the three pillars of the exposure triangle alongside aperture and ISO. Fast shutter speeds (1/500 s or shorter) freeze motion; slow speeds (1/30 s or longer) create motion blur. The relationship follows the APEX system standardized by ANSI/ISO. For more on exposure fundamentals, see our exposure calculator and depth of field calculator.
Exposure Value (EV) Reference Scale
The Exposure Value is a dimensionless number representing scene brightness. EV 0 is defined as f/1 at 1-second exposure at ISO 100. Each +1 EV halves the exposure. Typical values: EV -7 (Milky Way), EV 0 (dim artificial light), EV 8 (floodlit sports), EV 12 (overcast day), EV 15 (bright sun), EV 16 (sand/snow in sun). The scale is described in ANSI standard PH2.7-1986. For further reading, visit the Cambridge in Colour exposure tutorial.
Formula Derivation and the APEX System
The formula t = (100 × N²) / (S × 2^EV) is derived from the APEX (Additive Photographic EXposure) system. N is the f-number, S is ISO, and EV is the scene exposure value. The factor 100 normalizes for the ISO 100 baseline. Rearranging gives: EV = log₂(N² / t) + log₂(S / 100). This is consistent with the Sunny 16 rule: at EV 15 (clear sun), correct exposure at f/16 and ISO 100 is approximately 1/100 s. For lens planning, see our camera field of view calculator. The ISO standard governing this is ISO 12232:2019.
Motion Blur, Camera Shake, and Shutter Speed Selection
Choosing the right shutter speed depends on your subject. For hand-held shooting, the reciprocal rule recommends a shutter speed faster than 1/(focal length) — e.g., 1/50 s minimum for a 50 mm lens. To freeze fast motion (athletes, birds), use 1/500 s or faster. For creative blur of flowing water, 1/4 to 2 seconds works well. Long exposures (30+ seconds) are used for star trails and light painting. Pair your shutter speed selection with our blink-free photo calculator to avoid blinking subjects. Nikon's exposure guide covers this in depth.
ISO and Aperture Tradeoffs
When you increase ISO by one stop (e.g., 100→200), you can increase shutter speed by one stop while maintaining the same exposure. Widening aperture by one stop also allows one stop faster shutter. This interplay defines the exposure triangle. Higher ISO adds digital noise; wider apertures reduce depth of field. Use our crop factor calculator to understand how sensor size affects equivalent aperture and our depth of field calculator for depth implications. Photography Life — ISO Explained is an excellent external reference.
Practical Shutter Speed Guide by Scene
Quick reference by scene: Milky Way/stars (EV -7, 20–30 s, f/2.8, ISO 3200); indoor portrait (EV 6, 1/60 s, f/2, ISO 800); outdoor portrait sunny (EV 15, 1/250 s, f/5.6, ISO 100); sports/action (EV 8–12, 1/500–1/1000 s, f/2.8, ISO 800–3200); landscape golden hour (EV 10–12, 1/30–1/125 s, f/8, ISO 100). Always use a tripod for exposures longer than 1/focal-length. Our focal length calculator can help you determine minimum hand-held shutter speed. For more tips, visit B&H Photo.
Quick Reference Card
Shutter Speed Quick Reference
Quick reference • Shutter Speed Calculator
t = (100 × N²) / (S × 2^EV)Valid range: EV -7 to 16; aperture f/1 to f/32; ISO 25 to 51200
Common Values
⚠ Watch Out
- •Exposures longer than 1/focal-length risk camera shake — always use a tripod for slow shutter speeds.
- •Very high ISO (>3200) adds significant noise — balance with aperture or accept noise for fast action.
- •Using very wide aperture (f/1.4) with fast shutter may still overexpose in bright sun — consider ND filters.
- •Long exposures (>30 s) can cause sensor heat noise — use dark-frame subtraction in post-processing.
Pro Tips
- →Use EV as a quick estimate: in bright sun (EV 15), f/16 and 1/ISO gives correct exposure (Sunny 16 rule).
- →For panning shots that blur the background but keep subject sharp, try 1/30–1/60 s.
- →In video mode, the 180° shutter rule sets shutter speed to 1/(2 × frame rate) for natural motion blur.
- →Bracket exposures ±1 stop when shooting landscapes to ensure at least one is correctly exposed.
FAQs
What is shutter speed?
Shutter speed is the length of time the camera shutter remains open, exposing the sensor to light. It is measured in seconds or fractions of a second. Faster speeds (e.g., 1/1000 s) freeze motion; slower speeds (e.g., 1 s) create motion blur.
What is Exposure Value (EV)?
EV is a numerical scale representing scene brightness as perceived by the camera. EV 0 is defined as f/1 at 1 second exposure at ISO 100. Each EV step doubles or halves the light. Sunny daylight is EV 15; starlight is around EV -7.
How does aperture affect shutter speed?
Aperture and shutter speed have a reciprocal relationship. Wider aperture (lower f-number) lets in more light, allowing a faster shutter speed. Narrower aperture (higher f-number) requires a slower shutter speed for the same exposure. The relationship is quadratic: halving the f-number quadruples the light.
How does ISO affect shutter speed?
Higher ISO increases sensor sensitivity, so less light is needed. This allows a faster shutter speed. However, higher ISO introduces noise. Doubling ISO allows you to double the shutter speed with the same exposure, maintaining correct brightness.
What shutter speed prevents camera shake?
The reciprocal rule states: use a shutter speed at least as fast as 1/(focal length in mm). For a 50 mm lens, use at least 1/50 s. With image stabilization, 2–4 stops slower may be possible. On a tripod, even very slow speeds produce sharp images.
What is the Sunny 16 rule?
The Sunny 16 rule is a guideline: in bright sunlight (EV 15), set aperture to f/16 and shutter speed to 1/ISO. For ISO 100, that's 1/100 s at f/16. This rule gives correct exposure without a meter on a bright sunny day and is consistent with the APEX formula.