Dive Table Calculator
Look up the no-decompression limit (NDL) on air for a single dive, using standard recreational table limits from 10 to 40m.
Single dive on air
Inputs
Table covers 10 - 40m. Max recreational depth: 40m.
Time from descent to start of ascent.
Your depth of 18m maps to the 18m table row (always round up to the next deeper table depth).
Results
What are dive tables?
Dive tables are mathematical tools developed to help recreational divers plan dives that avoid decompression sickness (DCS). The first decompression tables were published by the Royal Navy in 1908, based on J.B.S. Haldane's research into how nitrogen dissolves and comes out of solution in body tissues under pressure.
The PADI Recreational Dive Planner (RDP), introduced in 1988, was specifically designed for no-decompression recreational diving. Unlike military tables, the RDP uses a multi-tissue model and builds in conservative safety margins to reduce DCS risk for divers at all experience levels.
How to read the RDP
The RDP consists of three tables. Table 1 shows the no-decompression limit (NDL) for each depth and assigns a pressure group letter (A through N) based on your bottom time. The further into the alphabet, the more nitrogen you are carrying.
To use Table 1: find the column for your depth (or the next deeper depth if yours isn't listed), then read down to find the row where your bottom time first appears. The pressure group letter in that cell is your group at the end of the dive.
Always round your depth up to the next table depth - never interpolate down. Similarly, round your bottom time up to the next minute if it falls between entries.
Repetitive dive planning
After a dive, nitrogen remains dissolved in your tissues. This residual nitrogen reduces your no-decompression time on subsequent dives. The RDP accounts for this through pressure groups and a surface interval credit.
Table 2 of the physical RDP card tracks how your pressure group decreases over a surface interval. Table 3 then shows your Residual Nitrogen Time (RNT) - the number of minutes you must add to your actual bottom time when looking up your new pressure group on Table 1. This tool doesn't do repetitive-dive planning: use the official tables you trained on or your dive computer.
Key rules for repetitive dives: always plan the deepest dive first, use the full surface interval credit before diving again, and be more conservative with multiple dives in a day (three or more dives significantly increases DCS risk).
Tables vs dive computers
Modern dive computers track multi-tissue nitrogen loading continuously throughout a dive, giving a more accurate and often more permissive NDL than static tables. However, tables remain essential for several reasons:
- Backup planning: If your computer fails mid-dive, you need to know how to surface safely.
- Pre-dive planning: Tables help you confirm your dive plan before you enter the water.
- Education: Understanding tables builds the conceptual knowledge needed to use a computer correctly.
- Certification requirement: All major agencies (PADI, SSI, BSAC) require divers to demonstrate table proficiency.
Never plan your dive solely on a calculator or app - always cross-reference with your actual dive computer in the water and follow the more conservative of the two limits.