Dive Decompression Calculator

Dive Decompression Calculator. Plan your scuba dives safely by entering your dive depth, bottom time, and surface interval to calculate required decompression stops and your pressure group. The Dive Decompression Calculator uses PADI-based recreational dive table logic — enter values for a single dive or a repetitive dive profile with a second depth to see your no-decompression limits, required stop depths, and stop durations before surfacing. Also try the Swimming Pace Calculator.

Depth of First Dive *

Maximum depth reached during the dive in metres.

Bottom Time of First Dive *

min

Total time from descent to beginning of ascent.

Surface Interval (Hours)

Hours spent on the surface between dives.

Surface Interval (Minutes)

min

Minutes spent on the surface between dives.

Depth of Second Dive

Leave 0 if planning only a single dive.

Ascent Rate *

Maximum recommended ascent speed.

Perform Safety Stop? *

Recommended for all dives deeper than 10 m.

Results

NDL Remaining (First Dive)

Pressure Group After Dive 1

Pressure Group After Surface Interval

Adjusted NDL for Second Dive

Decompression Stop Required?

Deco Stop Depth

Deco Stop Time

Total Ascent Time

Results Table

What is a no-decompression limit (NDL)?

The no-decompression limit is the maximum time you can spend at a given depth without needing mandatory decompression stops before surfacing. Exceeding the NDL means your body has absorbed enough nitrogen that a controlled decompression ascent is required to avoid decompression sickness (DCS). See also our calculate Recommended Pound Test, Estimated Line Diameter & Diameter (mm) — Fishing Line Strength.

What is a pressure group and why does it matter?

A pressure group is a letter (A–Z in PADI tables) that represents the residual nitrogen level in your body after a dive. It determines how long you need to wait on the surface before your next dive and how the NDL for that second dive is reduced. Higher letters mean more residual nitrogen.

What is a safety stop and is it mandatory?

A safety stop is a 3-minute pause at 5 metres during ascent. While not mandatory for dives within NDL limits, PADI strongly recommends it for all dives deeper than 10 m. It provides an extra buffer for off-gassing nitrogen and significantly reduces the risk of decompression sickness.

What is the recommended ascent rate for recreational diving?

PADI recommends ascending no faster than 9 metres per minute (approximately 30 feet per minute). Ascending too quickly doesn't give your body enough time to release dissolved nitrogen gradually, which can lead to bubble formation and decompression sickness.

How long should my surface interval be between two dives?

A minimum surface interval of 1 hour is generally recommended between recreational dives. Longer surface intervals reduce your pressure group, which increases the NDL for your next dive. A surface interval of at least 3 hours is recommended before flying after diving.

Can I use this calculator for dives deeper than 40 metres?

This calculator is based on PADI recreational dive tables, which cover depths up to 40 metres (130 feet). Dives beyond this depth fall into technical diving territory and require specialised training, equipment, and decompression software such as Bühlmann algorithm-based dive computers.

What happens if I exceed the no-decompression limit?

If you exceed the NDL, you must make one or more mandatory decompression stops at specified depths before surfacing. Skipping these stops risks decompression sickness (the bends), a potentially serious condition caused by nitrogen bubbles forming in the blood and tissues.

Is this calculator a substitute for a certified dive computer?

No. This tool is based on simplified PADI dive table logic for educational and planning purposes only. Always dive with a calibrated dive computer, follow your dive professional's guidance, and never exceed the limits of your certification level.