What do GF low and GF high do?

GF-low sets how much supersaturation you allow at the deepest (first) stop — lower means deeper stops. GF-high sets the supersaturation allowed at the surface — lower means more shallow-stop time before you surface.

What are common gradient-factor settings?

30/85 and 40/85 are common general-purpose settings; more conservative divers use lower values. There is no single correct pair — it depends on the dive, the diver and agency guidance.

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Gradient factors explained

Gradient factors are how you add conservatism to a Bühlmann decompression plan. They're written as a pair — GF-low / GF-high, e.g. 30/85 — and once you understand the two numbers, the whole shape of your ascent makes sense.

The M-value, in one sentence

Bühlmann's model gives each tissue a maximum tolerable inert-gas pressure at a given depth — the M-value. Diving exactly to the M-value (100%) is the model's theoretical limit. Gradient factors let you stay a chosen percentage below it.

GF-high: how hard you push at the surface

GF-high is the percentage of the M-value you allow when you surface. A GF-high of 85 means you surface at 85% of the limit. Lowering it keeps you down longer on the shallow stops, where most off-gassing happens — buying a safety margin where it counts.

GF-low: how deep your first stop is

GF-low is the percentage you allow at your first (deepest) stop. A lower GF-low forces you to begin decompressing deeper, adding "deep stops." Conservatism interpolates linearly from GF-low at the first stop to GF-high at the surface.

Common settings

30/85 and 40/85 — popular general-purpose settings.
Lower pairs (e.g. 20/80) add more conservatism and deeper stops.
There is no universally "correct" pair — it depends on the dive, your fitness and agency guidance.

Try it

The fastest way to build intuition is to change GF-low and GF-high on a real plan and watch the stops move. DecoLog's planner does exactly that, free.

Try it now — free, in your browser. • OPEN THE PLANNER

⚠ Educational only — not a substitute for training or a dive computer. Choose conservatism with proper instruction and verify every plan.