ND Filter Calculator

Q: What does this ND filter calculator output?

The large Final shutter speed label is the nearest camera 1/3-stop dial click. The Exact result panel below it shows computed seconds (often a decimal under 1 s, or h/m/s when longer). Total stops sums every row in the ND filter stack.

Q: How do I stack multiple ND filters?

Click + Add filter for each physical filter and pick stops from the preset list (1 stop / ND2 through 20 stops / ND1M). Stops add; remove extra rows with the trash icon when more than one filter is listed. See the educational example card for default stacking math.

Q: How does base shutter speed work?

Choose a preset from the Base shutter speed dropdown (1/64000 s through 30 s) or select Enter or find a custom exposure duration to type seconds, then use Back to presets to snap to the closest listed speed.

Q: When do bulb hint and exposure timer appear?

The bulb note shows when final time is above 30 s (strictly greater than 30). Start exposure timer is available at 30 s or longer. The timer counts down with vibration and a beep; it does not trigger the camera shutter.

Q: Is the math accurate for film?

Digital sensors follow Tfinal=Tbase×2nT_final = T_base × 2^nTfinal=Tbase×2n closely. Film can need extra time beyond that formula at multi-minute exposures (reciprocity failure). This calculator does not apply film-specific correction curves; check your emulsion data sheet for long exposures.

ND factor	Stops
ND2	1
ND4	2
ND8	3
ND16	4
ND32	5
ND64	6
ND128	7
ND256	8
ND1000	10
ND1M	20

Reading final shutter speed

Set the metered shutter without filters, stack ND strengths, then read the dial-friendly label and exact seconds before you touch the camera.

Example: 1/125 s base, 6 stops (default)

Defaults: base 1/125 s, one 6 stops (ND64) filter. Exact exposure = 1/125 × 2⁶ = 0.512 s (Exact result panel). The main readout rounds to 1/2 on the 1/3-stop scale. Total stops shows 6.

Red light mode and fullscreen

Toggle Red light mode at the top to preserve night vision; when it is on, open Full screen for a field-friendly layout. Calculations stay local in the browser with no network required.

Copy settings

Use Copy settings at the bottom of the results column for a one-line summary (base speed, total stops, final time) to paste into field notes or a messaging app.

ND filter shutter speed from stops

Final exposure = base shutter × 2^total stops, rounded to the nearest 1/3-stop camera setting, with stacking, a bulb hint above 30 s, and an optional countdown timer at 30 s or longer.

What this calculator returns

This calculator takes a metered base shutter speed and one or more ND filters in stops, sums the stops, and computes final exposure time. It does not set ISO or aperture, model vignetting from stacked filters, or apply film reciprocity correction.

Stacking:

Each filter row adds stops; presets run from 1 stop (ND2) to 20 stops (ND1M).
Density labels:

ND64 ≈ 6 stops because 2⁶ = 64; ND1000 ≈ 10 stops. Match your filter marking to the stop preset.

How the math works

Each stop halves light reaching the sensor, so exposure time doubles per stop.

T_{final} = T_{base} \times 2^{n}

With n = 9 stops (6-stop plus 3-stop stack), multiplier is 2⁹ = 512. Base 1/100 s becomes 0.01 × 512 = 5.12 s before dial rounding. Default outcomes at 1/125 s with 6 stops are in the educational example card.

Controls on this page

Left column inputs and right column results map as follows:

Base shutter speed:

Preset dropdown or custom seconds input.
ND filter strength:

Stackable rows with + Add filter; total shown under the list.
Final shutter speed:

Primary dial label plus Exact result and Total stops panels.
Red light mode / Full screen:

Top bar for night vision and fullscreen field layout.
Information hub:

In-widget tiles for stop math, ND factor versus stops table, shutter fraction scale, and brief film or DSLR field notes.

ND Filter Calculator FAQ

What does this ND filter calculator output?

The large Final shutter speed label is the nearest camera 1/3-stop dial click. The Exact result panel below it shows computed seconds (often a decimal under 1 s, or h/m/s when longer). Total stops sums every row in the ND filter stack.

How do I stack multiple ND filters?

Click + Add filter for each physical filter and pick stops from the preset list (1 stop / ND2 through 20 stops / ND1M). Stops add; remove extra rows with the trash icon when more than one filter is listed. See the educational example card for default stacking math.

How does base shutter speed work?

Choose a preset from the Base shutter speed dropdown (1/64000 s through 30 s) or select Enter or find a custom exposure duration to type seconds, then use Back to presets to snap to the closest listed speed.

Why does the dial label differ from exact result?

Cameras expose in fixed 1/3-stop steps. The headline rounds to the nearest dial value; Exact result keeps the computed time. Set the dial from the headline; use exact for bulb timing with the built-in timer.

When do bulb hint and exposure timer appear?

The bulb note shows when final time is above 30 s (strictly greater than 30). Start exposure timer is available at 30 s or longer. The timer counts down with vibration and a beep; it does not trigger the camera shutter.

Is the math accurate for film?

Digital sensors follow

T_{final} = T_{base} \times 2^n

closely. Film can need extra time beyond that formula at multi-minute exposures (reciprocity failure). This calculator does not apply film-specific correction curves; check your emulsion data sheet for long exposures.

Mathematical Reference Note

Calculation Logic: This tool uses standard mathematical algorithms. While we strive for accuracy, errors in logic or user input can result in incorrect data.

Verification: Results should be cross-checked if used for important academic, professional, or personal calculations.

Standard Terms: This tool is provided free of charge and as-is. CalcRegistry provides no warranty regarding the accuracy or fitness of these results for your specific needs.