How Do You Read a Recreational Dive Table?

What a dive table actually is

A recreational dive table is a printed chart that answers three questions: how long can I stay at a given depth on a first dive, how much nitrogen credit do I get back during a surface interval, and how much time do I owe against my next dive because of the nitrogen I'm still carrying. Most divers today rely on computers instead — see dive tables vs. dive computers for that comparison — but tables still show up in certification courses and exams, and understanding one makes everything your computer does far less mysterious.

Recreational tables descend from military decompression procedures; the U.S. Navy Diving Manual remains the classic government reference for the underlying system of limits, surface intervals, and repetitive-dive accounting. Training agencies adapted that framework into simpler, more conservative charts for recreational use, within the minimum training standards coordinated by the World Recreational Scuba Training Council.

The three parts of the table

Most recreational tables are really three linked charts:

Table 1 — first dive. Rows or columns of depths, with the maximum no-decompression time for each. You find your planned depth (always rounding up to the next listed depth), find your actual bottom time (rounding up again), and read off a letter — your pressure group, an estimate of how much nitrogen you absorbed.
Table 2 — surface interval. You enter with your pressure group letter and the length of your surface interval, and exit with a new, better letter. The longer you sit out, the more nitrogen you off-gas and the further down the alphabet you move.
Table 3 — repetitive dive. Your post-interval letter converts into residual nitrogen time for your next planned depth: minutes that count against you as if you had already spent them underwater. Subtract that from the depth's normal limit and you get your adjusted maximum bottom time.

That third step is the whole reason the terms repetitive dive and residual nitrogen exist: the table assumes your body still holds extra nitrogen from the earlier dive and shrinks your allowance accordingly.

A worked example, in words

Say you plan a morning dive followed by an afternoon dive:

After the first dive, you enter Table 1 at your depth and time and come out with a letter — call it a mid-alphabet group.
You spend a couple of hours on the boat. Table 2 slides you to an earlier letter.
For the afternoon dive, Table 3 tells you that at your planned depth, your letter equals a certain number of residual nitrogen minutes. Your usable bottom time is the depth's normal limit minus those minutes.

Every agency's table looks slightly different — different layouts, different letters, different conservatism — so the numbers only ever come from the specific table in your hand, used exactly as your course teaches it. The structure, though, is always this same three-step loop.

Rules that trip people up

Always round against yourself. Deeper than a listed depth means use the next deeper row; longer than a listed time means the next longer column.
Your deepest point sets your depth, even if you only touched it briefly. Tables treat the whole dive as if it happened at maximum depth — one reason computers, which track your actual profile, usually grant more time. Your no-decompression limit works the same way in both systems; the table just calculates it more bluntly.
Plan the deeper dive first. Tables (and standard practice reflected in references like the NOAA Diving Program) assume repetitive dives get progressively shallower, which keeps the residual-nitrogen math manageable.

Do you still need to learn this?

For real-world diving, a computer does all of the above continuously and less conservatively. But table questions still appear on certification exams, and the exercise teaches the one idea every diver needs in their bones: nitrogen accumulates, surface time pays it down, and the second dive is never a blank slate.