Flash Ratio Calculator
Master professional lighting ratios with our visual calculator. Perfect for portrait, product, and studio photography.
Ratio Calculator
Results
Select parameters and click "Calculate Ratio" to see results
Photography Note
These calculations provide lighting ratios based on power settings. Actual results may vary with modifiers, subject reflectivity, and camera settings.
Why Flash Ratios Scared Me (And Probably Scare You Too)
I remember the first time I tried using multiple flashes for a portrait shoot. I had this fancy camera, two expensive speedlights, and absolutely no clue what I was doing. The main light was blasting away at full power, and the fill light was set to... well, I wasn't sure. The results were hideous - faces that looked like they were half in shadow, half sunburned.
Turns out, I was creating what photographers call a "bad ratio." The main light was overpowering everything, creating harsh shadows that no amount of Photoshop could fix. I spent hours experimenting, burning through batteries, and getting frustrated. But here's the thing - once I understood ratios, everything clicked.
Flash ratios aren't some mystical photography voodoo. They're just a simple way to describe how much brighter one light is compared to another. And once you get it, you'll wonder how you ever shot without understanding them.
What Even IS a Flash Ratio?
Let's say you're cooking spaghetti. Your main light is like the big pot of boiling water - that's your key light, providing the majority of the illumination. The fill light is like adding a little olive oil to keep things from sticking - it fills in the shadows but doesn't overpower the main event.
A 3:1 ratio means your main light is three times brighter than your fill light. That might sound complicated, but think about it this way: if your main light is at full power and your fill light is at 1/3 power, you've got a 3:1 ratio. The shadows aren't completely black, but they're definitely there for dramatic effect.
Why not just say "brightness"? Because ratios are consistent regardless of how powerful your lights are. A 3:1 ratio looks the same whether you're using tiny speedlights or massive studio strobes.
The Math That Actually Makes Sense
Power Settings Explained
Flash power settings are usually expressed in fractions: Full, 1/2, 1/4, 1/8, etc. Each step represents a halving of the light power.
Converting Power to Ratios
Ratio = Power₁ ÷ Power₂
Where Power₁ is your main light and Power₂ is your fill light. Higher numbers mean more contrast.
Stop Differences
Stop Difference = log₂(Ratio)
A 4:1 ratio equals 2 stops difference. Each stop doubles or halves the light.
Example: 3:1 Ratio
Main light at 1/2 power (0.5), Fill light at 1/8 power (0.125). Ratio = 0.5 ÷ 0.125 = 4:1. Wait, that doesn't match! Actually, ratios are usually expressed with the smaller number as 1, so this is really a 4:1 ratio. The main light is 4 times brighter than the fill.
Distance Changes Everything
Light falls off according to the inverse square law. Double the distance, quarter the light. Move your light twice as far from the subject, and you need four times the power to maintain the same exposure.
This is huge for ratios. If your main light is 4 feet from the subject and your fill is 8 feet away, the main light will be four times brighter (2:1 ratio) without changing any power settings. Physics does the work for you!
Distance Ratio Formula
Ratio = (Distance₂ ÷ Distance₁)²
Where Distance₁ is the closer light and Distance₂ is the farther light.
The Five Ratios Every Photographer Should Know
1:1 (Flat Lighting)
Both lights equal. Great for passport photos, but can look flat and boring for portraits.
2:1 (Beauty Lighting)
Main light twice as bright. Soft, flattering look perfect for beauty and fashion work.
3:1 (Classic Portrait)
Main light three times brighter. Professional look with visible but not harsh shadows.
4:1 (Dramatic)
Main light four times brighter. High contrast, moody portraits with strong shadows.
8:1 (High Contrast)
Main light eight times brighter. Extreme drama, almost silhouette-like shadows.
| Ratio | Stop Diff | Best For | Mood |
|---|---|---|---|
| 1:1 | 0 stops | Corporate, products | Flat, even |
| 2:1 | 1 stop | Beauty, fashion | Soft, flattering |
| 3:1 | 1.6 stops | Portraits | Professional |
| 4:1 | 2 stops | Editorial | Dramatic |
| 8:1 | 3 stops | Artistic | High contrast |
How to Actually Use This in Real Life
Start with one light. Get your exposure right with just the main light. Then add your fill light at a lower power. Take a test shot. Too flat? Increase the ratio. Too harsh? Decrease it. Simple as that.
Don't get caught up in the math. Use this calculator to get in the ballpark, then fine-tune by eye. Your camera's LCD is the best light meter you'll ever own.
Common mistake: People set their fill light too bright. Remember, the fill should fill shadows, not eliminate them. Start with your fill 2-3 stops lower than your main light.
Quick Cheat Sheet and FAQ
Common Questions
What's the difference between ratio and stop difference?
Ratio compares light intensities directly (3:1 means main light is 3x brighter). Stop difference is logarithmic - each stop represents a doubling of light.
Do modifiers affect ratios?
Yes! Softboxes and umbrellas reduce light output, so you'll need to compensate with power settings. A large softbox might cost you 1-2 stops.
What's the "perfect" ratio?
There isn't one. 3:1 works for most portraits, but beauty work might use 2:1, and dramatic shots go to 8:1. It depends on your vision.