No-stop limits and gradient factors explained
A no-stop limit is the time you can stay at a depth and still ascend straight to the surface. A gradient factor decides how much margin that limit keeps. Both fit on one page.
What a no-stop limit is
Your body takes up nitrogen at depth, and the longer you stay, the more it holds. The no-stop limit is the time at a depth after which the model no longer allows a direct ascent: you would owe decompression stops. Loggerfish works it out with the Bühlmann ZH-L16C model, the same family many dive computers use.
What a gradient factor does
Bühlmann gives every tissue a maximum overpressure it tolerates. A gradient factor is the share of that limit a plan allows. GF 85 lets the tissues reach 85 % of it; GF 70 leaves more margin and shortens the limit; GF 95 allows more. Loggerfish offers those three.
At 30 m on air, the same dive gives three different answers:
| Gradient factor | No-stop limit at 30 m on air |
|---|---|
| GF 95 | 14 min |
| GF 85 | 12 min |
| GF 70 | 8 min |
The limits at a glance
At GF 85, the limit shrinks quickly with depth, and nitrox stretches it:
| Depth | Air | EAN32 |
|---|---|---|
| 18 m | 43 min | 72 min |
| 24 m | 20 min | 35 min |
| 30 m | 12 min | 19 min |
| 40 m | 6 min | 9 min |
Try it with your numbers
The calculator starts on 10 minutes at 30 m on air at GF 85. Move the minutes past 12 and the ring fills, then turns to a warning.
- No-stop limit at this depth, at sea level
- 12 min
- No-stop time left after your planned time
- 2 min
- Surfacing load, of the controlling compartment’s limit at GF 85
- 92%
Inside the no-stop limits at GF 85, with a normal ascent and a safety stop.
What the number does not tell you
- It is for one dive from the surface. A repeat dive, or a day of diving, starts with gas already in your tissues.
- Two computers with the same GF can still differ, if their models do.
- It is a plan. Underwater you follow your own dive computer, which tracks the dive you actually do.
These calculations are planning aids, not a dive computer. Your training and your computer decide the dive.
Check your no-stop time in Loggerfish
Free to start, no card. Your logbook, and every export of it, stays yours on every plan.
Names such as PADI, SSI, MySSI, Subsurface, MacDive, Shearwater and Garmin belong to their owners and are used only to say which product we mean. Loggerfish is not affiliated with any of them. What a guide says about them comes from their own public pages, listed beside the statement with the day it was checked. If something is out of date, write to support@loggerfish.com and we will correct it.