How big should my softbox be?

A general rule is the softbox should be at least as large as your subject. For headshots, a 60-80cm softbox works well. For half-length portraits, 90-120cm. For full-length, 120-180cm. Larger softboxes produce softer light with smoother shadow transitions.

Does distance affect softness?

Yes, dramatically. A softbox closer to the subject appears larger (relative to the subject) and produces softer light. Moving the same softbox further away makes it appear smaller, producing harder light. The apparent size (softbox size / distance) determines softness, not the physical size alone.

What is the apparent size of a light source?

Apparent size is the angular size of the light source as seen from the subject. The sun is a large light source but appears small (0.5°) because of its distance, producing hard shadows. A 120cm softbox at 1m has a much larger apparent size, producing soft shadows. Apparent size = modifier size / distance.

Softbox vs umbrella — which is softer?

At the same size and distance, they produce similar softness. Softboxes offer more control (less spill, can add grids). Umbrellas are lighter, cheaper and set up faster. Shoot-through umbrellas are slightly softer than reflective ones. For the softest light, use the largest modifier you can place as close as possible.

PhotoCalcs

Softbox Size Calculator — Ideal Modifier Size

Find the ideal softbox size for your subject and light-to-subject distance.

Subject Width

Width of your subject

Light-to-Subject Distance

Softbox to subject

How We Calculate This

This calculator recommends softbox size based on subject size and distance:

Ideal Size

Softbox size ≈ 1.2 x subject width

Apparent Size Ratio

Apparent size = softbox size / distance

Wrap Angle

Wrap = 2 x arctan(softbox size / (2 x distance))

Frequently Asked Questions

Related Calculators

Flash Guide Number Calculator

Calculate flash guide number from power, distance and aperture. Work out maximum flash range for any ISO and aperture setting. Free online calculator.

Inverse Square Law Calculator

Calculate how light intensity falls off with distance using the inverse square law. Essential for positioning studio lights accurately. Free online calculator.

Key to Fill Ratio Calculator

Calculate lighting ratios between key and fill lights for portrait photography. Dial in the right contrast and mood for studio setups. Free online calculator.

Light Falloff Calculator

Calculate light intensity drop-off across a scene or group of subjects. Position lights to achieve even illumination across the frame. Free online calculator.

Flash Duration Calculator

Estimate flash duration at different power settings for freezing motion. Find t.1 and t.5 times to plan high-speed photography. Free online calculator.

Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.