ABC Tools

Climbing Grade Conversion, Explained

After reading this you can move a climb between the Yosemite Decimal System, French, UIAA and Ewbank scales for routes, and between the V-scale and Fontainebleau for boulders, and you will know how much to trust the number you get.

What the converter does and one example

Climbing grades measure difficulty, but no country agreed on a single scale. A route in California carries a YDS number like 5.12a. The same moves in France read as 7a+, in Germany as UIAA VIII+, and in Australia as an Ewbank 25. The converter lines these systems up so one input gives you the others.

Here is the hook. You climbed a sport route abroad graded French 6c. Your logbook uses YDS. The converter maps 6c to 5.11a/b and Ewbank 22. That single conversion is the whole job, but the interesting part is why it can be off by a full letter grade, and this article explains that.

The four route scales and how they behave

Each route scale grows in a different shape, so understanding one number means understanding how its scale is spaced.

YDS (Yosemite Decimal System)
American. The climbing part is the fifth class, written 5.x. From 5.10 up, each number splits into letters a, b, c, d. So 5.10a is easier than 5.10d, and 5.11a follows 5.10d.
French
A number plus a letter plus an optional plus: 6a, 6a+, 6b. Widely used for sport climbing worldwide.
UIAA
Roman numerals with plus and minus, common in Germany and the Alps: VII, VII+, VIII-.
Ewbank
Australian and New Zealand. A single open-ended integer that keeps climbing: 18, 25, 32. No letters, no ceiling.

The key difference is resolution. Ewbank uses one integer per step, so its numbers rise faster than YDS letters. Between YDS 5.10a and 5.11a there are four letter steps (a, b, c, d, then a). Over that same span Ewbank moves roughly from 18 to 22, also four steps. The scales are close to parallel in the middle but drift apart at the ends.

UIAA is the coarsest of the four in the hard grades. Above UIAA XI the scale is rarely used, so the converter leans on YDS and French for anything past 5.14.

The mapping is a table, not a formula

There is no clean equation from YDS to French because the scales were built by different communities at different times. What exists is an agreed lookup table, and the converter stores that table as an ordered list of rows. Each row is one difficulty step.

You can still describe the relationship with a rough linear fit, which helps you sanity check a conversion. If you index the YDS letter grades starting at 5.10a = 0, and index French grades starting at 6a = 0, the two indices track each other almost one to one in the range 5.10a to 5.12d.

i_{\text{French}} \approx i_{\text{YDS}} + c

Here i_{\text{YDS}} is the step number in the YDS letter sequence, i_{\text{French}} is the step number in the French sequence, and c is a small offset that shifts by about one step across the useful range because French plus-grades and YDS letters do not partition difficulty identically. The approximation is good to within one step in the middle grades and worse at the extremes, which is exactly where you should stop trusting arithmetic and read the table.

Worked example: the demo defaults

Converting 5.10a in route mode

The demo button loads Routes mode with the route grade set to the option labelled 5.10a / 6a. Reproduce it and read across.

  1. Set discipline to Routes and pick the 5.10a / 6a row. This is index 4 in the route list.
  2. Read the YDS value: 5.10a. This is the entry grade to the letter-subdivided part of YDS, the point where climbers start caring about a, b, c, d.
  3. Read the French value: 6a. In many guidebooks 5.10a maps to 6a, though some tables shade it toward 5.9.
  4. Read the UIAA value: this row sits near VI+ to VII-.
  5. Read the Ewbank value: about 18 to 19.

So one climb reads as 5.10a, 6a, VI+, Ewbank 18. Every one of those describes the same rock. The spread you see (VI+ vs VII-) is the honest uncertainty, not a bug.

When a guidebook gives a grade with a slash, like 6a+/6b, treat it as one half-step and log the harder side if the crux felt hard. Averaging two logs at the lower grade will quietly inflate your apparent volume at that grade.

Boulders: V-scale and Font diverge in the middle

Bouldering uses two scales. The American V-scale runs VB, V0, V1 upward as integers. The Fontainebleau scale runs 4, 5, 6A, 6A+, 6B upward with letters and pluses. They agree at the ends and disagree most in the mid grades.

The demo default for boulders is V3 / Font 6A / 6A+. Notice the single V grade maps to two Font grades. That is the divergence in action: one V-step spans more than one Font step around here. Higher up, V9 maps to 7B+/7C, again spanning two Font grades.

Selected boulder conversions showing where one V-grade covers two Font grades
V-scaleFontSpread
V36A / 6A+two Font steps
V46B / 6B+two Font steps
V56C / 6C+two Font steps
V67Aone Font step
V97B+ / 7Ctwo Font steps

A practical consequence: a problem posted as Font 6C can feel like V4 or V5 depending on whether it rewards finger strength or body tension. The footnote on the tool page says the same thing, and the widget below lets you feel it.

Each V-grade against a Font step index where every letter and plus counts as one step. The straight line is a constant ratio. The points bow away from it in the middle, which is where one V-grade covers two Font grades.

Reading the result without overtrusting it

The converter gives a point estimate. Attach an error bar in your head. In the mid route grades the honest uncertainty is about half a letter, so a converted 5.11c could be logged as 5.11b or 5.11d by another climber on another day. For boulders in the 6A to 7A Font band, expect a full V-grade of disagreement.

Rock type and style shift the number too. Vertical technical limestone tends to feel softer in French terms than steep pocketed rock at the same grade. The scales encode consensus, and consensus varies by crag.

Without JavaScript: pick any route grade in the tool and note the converter often shows a range on the French or Ewbank side. That range is the real spread. In the mid grades it is about half a letter for routes and about one full V-grade for boulders.

Common mistakes

The errors below cost people real accuracy in their logbooks.

  • Treating the conversion as reversible to the exact grade. Converting 5.11a to French 6c and back can land you on 5.11b because of rounding across the table. Log the original grade, convert only for display.
  • Mixing route and boulder scales. V-grades and YDS measure different things (a boulder problem versus a roped route). A V5 is not a 5.12. The converter keeps them in separate modes for this reason.
  • Reading a slash grade as an average. Font 6C shown as V4/V5 means the community disagrees, not that the true value is V4.5.
  • Assuming UIAA extends cleanly into the hardest grades. It does not see much use above XI, so those rows are the least reliable.

Related tools

Two other calculators on this site touch the same athletes. The Ape Index Calculator gives your wingspan minus height, the reach metric that partly explains why a reachy 6b can feel like 6c to a shorter climber. If you also ski, the Ski Binding DIN Calculator converts your weight, height, age and boot length into an ISO release value the same way this tool converts grades: by a standard table, not by guesswork.

Frequently asked questions

Is 5.12a the same as 7a or 7a+?

Most tables place 5.12a at 7a+, with the boundary near 7a+/7b. The converter shows that shading rather than forcing a single French grade, because guidebooks disagree by about half a letter here.

Why does one V-grade equal two Font grades?

The V-scale uses one integer per step while Font inserts letters and pluses, so Font has finer resolution in the mid range. Around V3 to V5, one V-step covers two Font steps, for example V3 = 6A/6A+.

Can I convert a route grade to a boulder grade?

No, and you should not. Routes and boulder problems test different things over different lengths. Keep the discipline set correctly and compare like with like.

How accurate is the Ewbank conversion?

Good to about one Ewbank number in the mid grades. Ewbank 18 sits near 5.10a, and each further YDS letter adds roughly one Ewbank point up to the low 20s, after which the spacing loosens.

Which scale should I record in my logbook?

Record whatever the guidebook or gym used, then convert for display only. Converting first and logging the converted value bakes the table's rounding error into your history.

Try it yourself in the tool

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