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Gradient Factors

The Gradient Factors calculator estimates the No Decompression Limit (NDL) for a given depth and gas mix using the Buhlmann ZH-L16C decompression algorithm. It lets you see how different gradient factor settings affect your available bottom time.

Free Tool

The Gradient Factors calculator is completely free and does not require an account.

How it works​

Gradient factors (GF) control how conservatively the Buhlmann algorithm calculates decompression limits:

  • GF Low controls how close to the M-value the algorithm allows at the deepest decompression stop. A lower value means the first stop happens earlier and deeper.
  • GF High controls how close to the M-value you are allowed to be when you reach the surface. A lower value means longer overall decompression.

In simple terms: lower values = more conservative (longer deco obligations, wider safety margin), and higher values = more aggressive (shorter deco, less margin).

Inputs​

  • Dive depth -- the planned maximum depth
  • O2 percentage -- the oxygen fraction of your breathing mix
  • GF Low -- low gradient factor (10--100%)
  • GF High -- high gradient factor (10--100%)
  • Altitude -- elevation of the dive site
  • Water type -- fresh or salt water

Output​

The calculator returns an estimated NDL in minutes. At very shallow depths where decompression is not a concern, the NDL may display as infinite.

Gradient Factors calculator with preset buttons and NDL resultGradient Factors calculator with preset buttons and NDL result

Full Gradient Factors calculator showing preset buttons, inputs, and NDL result -- calc-gf-overview-light.png / calc-gf-overview-dark.png

GF presets​

Six preset gradient factor combinations are available as quick-select buttons:

PresetGF Low / GF HighConservatism
30/7030% / 70%Very conservative
35/7535% / 75%Conservative
40/8040% / 80%Moderate
45/8545% / 85%Standard
50/9050% / 90%Liberal
55/9555% / 95%Aggressive

Clicking a preset immediately updates the GF values and recalculates the NDL.

Custom GF sliders​

If none of the presets match your preference, use the custom sliders to set GF Low and GF High independently. The sliders allow fine-grained control from 10% to 100%.

Custom GF slider controlsCustom GF slider controls

Close-up of the custom GF Low and GF High slider controls -- calc-gf-sliders-light.png / calc-gf-sliders-dark.png

Educational Tool

This calculator is for educational purposes. Always use a dive computer with appropriate GF settings for actual dives.