NDL Calculator

Enter the depth and the gas to see the no-decompression limit for the first dive of the day. The Bühlmann model, the US Navy table and DECO 2000 are shown next to each other.

Results update as you type.

Depth (m)

That is 59 ft. Use the deepest point of the dive.

Gas

Nitrox carries less nitrogen than air, so its limit is longer. Its MOD at ppO₂ 1.4 bar is the deepest you can take it.

Conservatism (gradient factors)

The same presets as our deco planner. Only GF High, the second number, changes the no-stop limit, and a lower GF High is more conservative.

No-decompression limit, Bühlmann ZHL-16C

First dive of the day

At 18 m (59 ft) on Air, the Bühlmann model at GF 40/85 allows 47 minutes of bottom time with a direct ascent and no required stops.

Bühlmann ZHL-16C, GF 40/85: 47 min
US Navy Rev 7 (60 ft row): 63 min
DECO 2000 (18 m row): 45 min

NDL table by depth for Air

No-stop limits for the first dive of the day at each DECO 2000 depth row, worked out with the gas and gradient factors picked above. The row your depth falls into is highlighted.

No-decompression limits in minutes by depth for Air: Bühlmann at GF 40/85, US Navy Rev 7 and DECO 2000
Depth	Bühlmann GF 40/85	US Navy Rev 7	DECO 2000
12 m(39 ft)	131	163(40 ft row)	140
15 m(49 ft)	71	92(50 ft row)	72
18 m(59 ft)	47	63(60 ft row)	45
21 m(69 ft)	33	48(70 ft row)	31
24 m(79 ft)	24	39(80 ft row)	23
27 m(89 ft)	19	33(90 ft row)	18
30 m(98 ft)	15	25(100 ft row)	15
33 m(108 ft)	13	20(110 ft row)	12
36 m(118 ft)	11	15(120 ft row)	10
39 m(128 ft)	9	12(130 ft row)	9
42 m(138 ft)	8	10(140 ft row)	7

US Navy depths are converted at 1 ft = 0.3048 m and read in the next deeper row of Table 9-7, so 18 m (59 ft) uses the 60 ft row. On nitrox the row is found from the EAD. Bühlmann values assume an 18 m/min descent that counts as bottom time and a direct ascent at 9 m/min.

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These tools are educational planning aids; they are not a substitute for dive training, current printed tables or a dive computer. Verify results against your training and always plan within the limits of your certification.

About the no-decompression limit

The no-decompression limit (NDL), also called the no-stop limit, is the longest time you can stay at a depth and still ascend straight to the surface without required decompression stops. Bottom time starts when you leave the surface and ends when you leave the bottom.

Each table and model accepts a different level of risk, which is why the three numbers here differ. All of them are for the first dive of the day.

With your numbers

Enter valid values to see the calculation worked through with your numbers.

Formula

No-stop rule (Bühlmann with GF High)

Ptol = (Pt − GFhigh × a) ÷ (GFhigh ÷ b − GFhigh + 1) ≤ Psurface

Equivalent air depth (EAD)

EAD = (((1 − FO2) × P) ÷ (0.79) − 1) × 10

Maximum operating depth (MOD)

MOD = ((1.4) ÷ (FO2) − 1) × 10

US Navy row

dft = (d) ÷ (0.3048), row = first table depth ≥ dft

Where

Pt: nitrogen pressure in a tissue compartment at the surface after a direct ascent (bar). a, b: its Bühlmann coefficients
GFhigh: GF High as a fraction (85% = 0.85). Psurface: 1.01325 bar
FO2: oxygen fraction (EAN32 = 0.32). P: absolute pressure, (d) ÷ (10) + 1 (bar). d: depth (m)
NDL: the longest whole-minute bottom time for which the rule holds in every compartment

How it's calculated

Bühlmann: the same engine and settings as our scuba deco planner. ZHL-16C nitrogen coefficients with compartment 1b, 1.01325 bar at the surface plus 1 bar per 10 m, 0.0627 bar water vapour, and tissues saturated with surface air at the start.
Profile: an 18 m/min descent that counts as bottom time, then a direct ascent at 9 m/min. The NDL is the longest whole-minute bottom time for which the ascent reaches the surface without passing GF High. GF Low only places stops, so it does not change the NDL. Limits longer than 360 minutes are shown as over 360.
US Navy: Rev 7 Change A, Table 9-7. Metres are converted at 1 ft = 0.3048 m and read in the next deeper row, as in our US Navy planner. On nitrox the row is read at the EAD, rounded up to 0.1 m. The 10-20 ft rows have no limit.
DECO 2000: the no-stop limit of the next deeper depth row (12-42 m). Depths shallower than 12 m use the 12 m row. DECO 2000 is an air table, so on nitrox it is read at the EAD, like the US Navy column.
MOD: ppO₂ 1.4 bar, rounded down to 0.1 m (air 56.6 m, EAN32 33.7 m, EAN36 28.8 m). Deeper than that, no NDL is shown.
Cross-check: on air at 12-42 m and on EAN32 at 15-33 m (Bühlmann and DECO 2000 at EAD), every value matches the tables in our guide to no-decompression limits.

Good to know

The NDL is for the first dive of the day. On a second dive, nitrogen from the first one shortens it, so use the repetitive dive tab of the DECO 2000 or US Navy planner, or your dive computer.
Dive computers differ. Each brand runs its own algorithm and conservatism setting, so two computers on the same dive can show different limits. On the dive, follow your own computer.
Leave a margin. Cold water, hard work and several dives a day are reasons to stay well inside the limit.
Bühlmann and US Navy values are for sea level, and DECO 2000 is valid up to 700 m of altitude. For a mountain lake, start with the altitude diving calculator.
This is a planning aid. It does not replace dive training or a dive computer.

Frequently asked questions

Why does the calculator show three different NDLs?

Each source accepts a different level of risk. The US Navy table was built for Navy divers, DECO 2000 is the more conservative table taught on CMAS courses, and the Bühlmann value depends on the gradient factors you pick. At 18 m on air they give 45 minutes (DECO 2000), 47 (GF 40/85) and 63 (US Navy). Plan with the table or computer you were trained on. The guide to no-decompression limits explains where the gap comes from.

How much does nitrox add to the no-decompression limit?

EAN32 carries 68% nitrogen against 79% in air, so the limit gets longer. At 18 m, Bühlmann at GF 40/85 gives 47 minutes on air and 82 on EAN32. Read at the EAD of 14.2 m, the US Navy table gives 92 minutes (50 ft row) instead of 63 (60 ft row). The price is a shallower MOD: 33.7 m for EAN32 at a ppO₂ of 1.4 bar.

Which gradient factor setting should I pick?

If your dive computer uses gradient factors, pick the same GF High so the numbers line up. GF 40/85 is the default in our deco planner. Only GF High changes the NDL: at 18 m on air, GF High 70 gives 33 minutes, 80 gives 42, 85 gives 47 and 100 (the raw model with no margin) gives 63.

Can I use this NDL for my second dive of the day?

No. Nitrogen from the first dive is still in your tissues, so the next dive has a shorter limit. Work it out with the repetitive dive tab of the DECO 2000 planner or the US Navy planner, or follow your dive computer, which carries the loading over.

How to use the NDL calculator

1
Enter the deepest depth you plan to reach. The same depth in feet appears under the box.
2
Pick your gas. For a nitrox mix other than EAN32 or EAN36, choose Other nitrox mix and type its oxygen percentage.
3
Pick a gradient factor preset, then read the three limits and the table below for nearby depths.

What the result means

The big number is the Bühlmann ZHL-16C limit with your gradient factors, the model behind many dive computers. Stay at that depth any longer and the model asks for decompression stops before you surface.

The US Navy and DECO 2000 figures come from printed tables, which round your depth up to the next row. DECO 2000 sits furthest from the edge: at 18 m on air it gives 45 minutes, the US Navy 63.

Planning 40 minutes at 18 m on air? Bühlmann at GF 40/85 gives 47 and DECO 2000 gives 45, so the plan fits both with little to spare. On EAN32 the Bühlmann limit at 18 m rises to 82 minutes.

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