Glossary
CFG Scale Guide
How to choose the right guidance scale value for any model to get sharp, properly-prompted images without burning the output.
CFG Scale (Classifier-Free Guidance Scale) controls the trade-off between prompt fidelity and generation diversity. Understanding how it interacts with different models is one of the highest-leverage skills in AI image generation.
How it works: the diffusion model simultaneously runs a conditioned pass (your prompt) and an unconditioned pass (blank/null prompt). The output is: unconditioned + CFG × (conditioned − unconditioned). A CFG of 1 means no guidance boost; you are getting pure diffusion. Higher CFG multiplies the difference, pushing the result harder toward the prompt.
Flux recommended ranges: Flux Schnell performs best at CFG 1–2 (it uses flow-matching and is already highly conditioned). Flux Dev: 3–4. Flux Pro: 3–5. Going above 6 on Flux causes over-saturation and loss of natural lighting.
SDXL recommended ranges: 5–9 for general photorealism. 7 is the community sweet spot. Above 12 produces harsh tonal compression and faces that look 'plastic'.
SD 1.5 recommended ranges: 6–10. Community checkpoints trained on specific aesthetics (anime, painterly) sometimes have shifted sweet spots — check the model card.
Practical tips: if your subject looks too generic or off-prompt, raise CFG by 1–2. If the image looks over-processed, burned, or plastic, lower CFG by 1–2. Adjust in small increments — the effect is non-linear.
Frequently Asked Questions
- What CFG should I use for photorealistic portraits?
- Flux: 3–4. SDXL: 6–8. These ranges tend to produce the most natural skin tones and lighting.
- Does CFG affect generation speed?
- No — CFG is a mathematical weighting applied to existing model outputs, not an additional model pass. It does not change inference time.
- What happens if I set CFG to 0?
- You get a completely unconditioned image — essentially random noise resolved without any prompt influence. Useful for testing but rarely intentional.
- Is CFG the same as 'guidance strength' in some UIs?
- Yes — guidance scale, CFG scale, and guidance strength are the same parameter with different labels depending on the interface.