Yosemite Decimal System: why 5.10 is harder than 5.9

5.10 is not 5.1

No other climbing scale is so reliably misread. The Yosemite Decimal System is called “decimal”, looks like a decimal number — and is not one. 5.9 is followed by 5.10, then 5.11, then 5.12. Arithmetically 5.10 would be smaller than 5.9; as a grade it is a full step above.

The reason lies in the structure: the number before the dot is a terrain class, the number after it a running number within that class. The dot separates two pieces of information; it does not mark a decimal place. Anyone who tips YDS grades into a spreadsheet finds that out quickly — the program sorts 5.10 before 5.9, because it calculates what the human does not mean.

First a scale for terrain, then one for climbing

The system does not begin on rock but on the walking path. It divides terrain into five classes, and only the fifth is climbing in the narrower sense.

Everything on the walls of a climbing gym is class 5. That is why every gym grade begins with a five, and why that five never changes. It does not say how hard the route is — it says that it is a route at all.

Ten routes on one crag in Southern California

In the 1950s, members of the Sierra Club in Southern California refined an older system from the 1930s. Royal Robbins, Don Wilson and Chuck Wilts subdivided the fifth class decimally: 5.0, 5.1 and so on up to 5.9.

This subdivision was anchored to ten routes at Tahquitz Rock — from “The Trough” of 1936 as 5.0 to “Open Book”, which Royal Robbins and Don Wilson free-climbed in 1952, as 5.9. The grades were first made known via duplicated circulars of the climbing section of the Sierra Club’s Los Angeles chapter; they were presented systematically for the first time in 1956, in Chuck Wilts’s Tahquitz guide.

That is the most remarkable feature of this scale: it was not derived from definitions like the UIAA scale, but from actual routes. The yardstick was not a description but a crag everyone involved had climbed on.

The name is wrong — and that is known

The scale came about and was standardised at Tahquitz, not in Yosemite Valley. Mark Powell brought it there at around the same time, and because Yosemite Valley became the best-known climbing area in the world over the following decades, its name stayed attached to the scale.

Before that it was simply called the “Southern California system” or the “Wilts-Sierra system”. Both names would be more accurate; neither stuck. Scales are named after what gets attention, not after where they come from.

Here too, 5.9 was meant to be the end

Open Book was given 5.9 because it was regarded at the time as the hardest climbing a human could manage without aid. The scale was thereby closed at the top — just like the UIAA scale at the sixth grade, and with the same result: it was climbed past.

At first people made do with 5.9− and 5.9+. When even that was no longer enough, 5.10 arrived — and with it the decimal logic that had given the system its name was finished. The scale sacrificed its own arithmetic in order not to have to stop at 5.9. It still carries that break visibly with it today.

Because a particularly large number of routes then piled up at 5.10, the suffixes were added in the early 1970s: from 5.10 upwards it is subdivided further with the letters a, b, c and d. Four steps per number — below that, up to 5.9, this fine gradation does not exist.

The number is only a third of the grade

The YDS is a three-part system. In German-speaking countries almost only the first part is ever quoted — the number. The other two parts answer questions that none of the European scales even asks: how bad the protection is and how long the whole thing takes.

Second: the protection. In 1980 Jim Erickson introduced codes that describe not the difficulty but what a fall means.

A 5.10a X and a 5.10a G demand the same movements. One route is a training day, the other a decision. That distinction is missing entirely from the French scale, which grades only climbing technique.

Third: the commitment. Roman numerals state how much time a route demands: I and II for half a day or less in the technical section, III for most of a day on the rope, IV for a full day of technical climbing, V for a route that usually requires an overnight stay or is climbed fast and free in a day, VI for two or more days of hard climbing and VII for remote walls in alpine style. A complete grade can therefore consist of a Roman numeral, a numerical grade and a protection code.

Anyone who grew up only with European scales easily mistakes a Roman numeral in front of a YDS grade for a UIAA grade. It is not one — it says nothing about difficulty, only about duration. Separately from that, aid climbing has its own series from A0 to A5, based on the number and quality of placements; if such a route is climbed without a hammer, a “C” takes the place of the “A”.

Open-ended: 5.15d

The highest grade awarded so far is 5.15d. It sits on three routes: Silence, first climbed by Adam Ondra in 2017, DNA by Sébastien Bouin from 2022 and B.I.G. by Jakob Schubert from 2023. None of the three has been repeated.

Three unrepeated routes at the top means the highest step of this scale consists of three individual opinions that cannot confirm each other. That is not a criticism of the scale but lies in the nature of the thing — a grade only becomes a yardstick through a second ascent.

Where you meet the scale today

Above all in the United States and Canada, but there throughout — from the gym to the walls of Yosemite Valley. Outside North America you will mostly meet the YDS in guidebooks, in video reports and in the numbers used to report international ascents.

For conversion the same applies as with the other scales: it is an approximation, and in some places the reference table gives no grade of its own on the other side between two YDS values. Which value corresponds to which is set out in full in the climbing grade converter — with ranges wherever the table offers no single value.

Frequently asked questions

Is 5.10 easier than 5.9?

No, harder — and that is the most common error with this scale. The number after the dot is not a decimal place but a running number. 5.9 is therefore followed by 5.10, then 5.11 and so on. It is read “five ten”, not “five point ten”. Arithmetically 5.10 would be smaller than 5.9; as a grade it is a full step above.

What does the 5 before the dot mean?

It stands for the fifth class of the system — technical free climbing on a rope. Before it lie four classes for terrain: walking, simple scrambling with occasional use of the hands, scrambling with an occasional rope, and simple climbing. Everything on the walls of a climbing gym is class 5; the number in front never changes.

What does R or X after a grade mean?

Those are protection ratings, not difficulty ratings. G stands for good protection, PG for adequate, R for inadequate — where a fall will probably cause injury — and X for none at all, where a fall will probably be fatal. These codes were introduced by Jim Erickson in 1980. A 5.10a X is technically the same climbing as a 5.10a G and yet an entirely different undertaking.

Why is it called Yosemite when it comes from Tahquitz?

Because the name stuck, not because it is accurate. The scale was developed and standardised at Tahquitz Rock in Southern California. Mark Powell brought it to Yosemite Valley at around the same time, and because that area became internationally known, its name stayed attached to the scale. It used to be called the “Southern California system” or the “Wilts-Sierra system”.

How far up does the scale go?

It is open-ended. The highest grade awarded so far is 5.15d. It sits on three routes: Silence by Adam Ondra from 2017, DNA by Sébastien Bouin from 2022 and B.I.G. by Jakob Schubert from 2023. None of them has been repeated.

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