How to Read a GTO Poker Chart

What a GTO chart actually shows

A solver is handed a precise question — six-handed, 100 big blinds deep, this rake, open-raise or fold from this seat — and plays it against itself until neither side can gain by changing strategy. What comes out is a frequency for every action with every hand. A chart is that table drawn as a grid.

The layout never changes. Pairs run down the diagonal, suited hands sit above it, offsuit hands below. The 169 squares stand in for 1,326 real two-card combinations: a pair is six combinations, a suited hand four, an offsuit hand twelve. That is why the “percentage of hands” figure printed on a chart is never the percentage of squares shaded — the offsuit region carries far more weight than its area suggests.

The caveat belongs at the top rather than the bottom. A chart answers one question, not a general one: change the stack depth, the player count, the rake or the action facing you and the answer moves with it. Both charts above ask the same question — open-raise or fold, 100bb, 6-max cash — and differ only in the seat.

Reading the colours

There are three states, and the third is the one people misread.

• Solid. A pure action. The solver takes it every single time.
• Empty. A fold. Not “sometimes” — never.
• Partly filled. A mixed strategy. The fill height is the frequency, so a square filled to 40% is raised 40% of the time and folded the other 60%.

Charts for spots with three live options — the big blind facing a raise, for instance — use one colour per action instead, usually raise, call and fold, and split a single square between two colours where the strategy is mixed. The reading is identical: colour tells you which action, area tells you how often.

Why solvers mix

A hand gets played two ways only when it is exactly indifferent between them — raising and folding are worth the same number of chips. Anything with a strict preference is played purely, which is why mixed hands cluster along the outer edge of a range and almost never appear in the middle of it.

The practical consequence is liberating. Because mixed hands are indifferent, the expected-value gap between the two actions is close to zero, so picking one and sticking to it costs a fraction of a big blind per 100 hands. Rounding is fine. Rounding everything upward is not — that is how a 20% opening range quietly becomes a 30% one.

Worked example: under the gun against the button

Both charts above come from the same solve, at the same stack depth, answering the same question. Under the gun the solver opens 16.6% of hands; on the button it opens 49.3%. Nothing about the cards changed. What changed is how many players are left to act and whether you are guaranteed the last word after the flop.

The top and bottom rows are unanimous and uninteresting: aces are raised from everywhere, 72 offsuit from nowhere. The rows in between are the entire lesson. Q9 suited and KT offsuit sit right on the boundary of the under-the-gun range, so the solver splits them; from the button they are comfortably inside the range and get raised every time. J9 offsuit is the mirror image — never opened under the gun, a genuine coin flip on the button.

Every partly-filled square is at the frontier of its range. That is the test of whether you have read a chart properly: you should be able to point at the edge without reading the numbers.

The six seats compared

The button opens roughly three times as many hands as under the gun, and that single ratio explains most of what separates a winning preflop game from a losing one. The small blind figure needs an asterisk: with only one player left to act, the solver raises a polarised range and limps a supporting one behind it, so the percentage shown is the raising half rather than the whole strategy.

How to practise with charts

• Learn the boundary, not the squares. Knowing where each range stops — which suited ace, which offsuit broadway — is one fact per row rather than thirteen, and it survives far longer than a memorised grid.
• One seat at a time. Trying to install six ranges at once produces six vague ones.
• Round the mixes, then audit the rounding. The hands you rounded up and the hands you rounded down should be roughly balanced.
• Test yourself on hands you actually played. Review your own opens against the position charts rather than re-reading them cold.

Opening ranges are the cheapest part of the tree to learn and the most expensive to get wrong, because every hand starts there. They are also where the chart runs out: once someone 3-bets, or the flop comes down, the answer stops being a grid and starts being a strategy per board. Reading full solver output is the next skill, and it is the same skill — find the indifference, find the edge of the range, ignore the noise in the middle.