Bouldering grade conversion calculator
V5 converts to 6C and a Font 7A comes back as V6: type a grade from either scale and get its counterpart from the consensus table climbers and guidebooks use, from VB up to V17. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Grade
- V5
- Grade input
- V5
- From scale
- v_scale
- V scale
- V5
- Fontainebleau
- 6C
Boulderers train and travel across regions that publish difficulty on different ladders. Gyms and outdoor guides in North America usually label problems with the Hueco V-scale, while European guidebooks and many international apps use the Fontainebleau scale. Comparing a V5 project at home with a 6C listed on a Font topo—or the reverse when packing for a trip—should not require hunting conversion charts in three tabs. Intermediate Font bands such as 6A+ and 7B+ map to the usual mid-band V grade so the response is always a concrete pair, never an open range.
How V-scale and Fontainebleau grades relate
The Hueco V-scale and the Fontainebleau scale are both ordinal ladders for bouldering difficulty, not continuous physical formulas. V-scale labels run from soft beginner problems often written VB or V0 up through elite V17, with each step intended as a clear jump in required strength, technique, or power endurance. Fontainebleau grades historically grew from the sandstone circuits outside Paris and now dominate European outdoor topos; they use numeric bands with letter and plus modifiers such as 6A, 6A+, 6B, and later 7C+ or 8A.
Because the two ladders were calibrated in different communities and rock styles, there is no laboratory identity between a V number and a Font label—only a widely reused consensus table that route-setters, guidebook authors, and apps consult when they need a one-line crosswalk. This capability encodes that consensus as a bidirectional lookup: each supported V grade has a preferred Font counterpart, and each supported Font grade maps back to a preferred V grade.
Intermediate Font grades that sit between whole V steps (for example 6A+ or 7B+) resolve to the V band most tables treat as the midpoint so automation always receives a single deterministic answer. That design matches how climbers actually talk about conversions in the gym—“about a V5”—while still giving scripts stable strings they can store, sort, and display. Soft grades such as VB and Font 3 cover the entry band; the upper end pairs V17 with Font 9A so elite problems stay on the chart without inventing unofficial steps.
Where a bouldering grade converter earns its keep
Traveling climbers constantly cross-check gym projects against outdoor lists when a Font week follows months of V-scale training; a trusted oracle that returns both labels in one shot removes chart-hunting friction between sessions. Training-log apps and spreadsheets need a deterministic map so a user who types V7 and a friend who logs 7A+ land on comparable progression charts. Guidebook importers and outdoor platforms that merge North American and European topos must normalize grades before filtering by difficulty band, and inventing ad-hoc mappings in every pipeline creates silent drift.
Coaches and route-setters who rotate between regions use the same table when explaining why a circuit feels softer or harder than the printed number after a style change. Failed validation does not consume balance. Keep requests small, pin the paired labels in automated tests, and you get reproducible conversions for trip planners, log exporters, and edge workers without scraping third-party charts.
Treat sport-route French grades, Yosemite Decimal System rope grades, and UK technical grades as separate search intents rather than overloading this bouldering-only converter.
What you can do with it
Trip planning across regions
Convert your home gym V-scale projects into Fontainebleau labels before a Font or Euro-sandstone trip, or the reverse when packing for US destinations.
Training logs and progression charts
Normalize mixed V and Font entries in a climbing diary so weekly volume and peak difficulty sort on one consistent ladder.
Guidebook and app data import
Map imported problem lists from multiple countries onto a single pair of labels for filters, search, and difficulty histograms.
FAQ
How do I convert a V-scale grade to Fontainebleau?
Send grade as a V token such as V5 or v10.
How do I convert a Fontainebleau grade to V-scale?
Send grade as a Font token such as 6C, 7A+, or 8A.
Are bouldering grade conversions exact?
No. The mapping is an approximate community consensus. Gym style, rock type, and local sandbagging can shift a problem roughly a band either way; the note field states this explicitly.
Which grades are supported?
V-scale VB and V0 through V17, and Fontainebleau 3, 4, 4+, 5, 5+, and 6A through 9A with optional plus on lettered bands.
What V grade is an in-between Font grade such as 6A+ or 7B+?
It maps to the V grade that most conversion tables treat as the middle of that band. That way you always get one concrete pair instead of a range, close to how climbers say about a V5 in the gym.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/hobby/sport-climb-boulder-convert \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"grade":"V5"}'const res = await fetch("https://api.kit.forhosting.com/hobby/sport-climb-boulder-convert", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"grade": "V5"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/hobby/sport-climb-boulder-convert",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"grade": "V5"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/hobby/sport-climb-boulder-convert", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"grade":"V5"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"grade":"V5"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/hobby/sport-climb-boulder-convert", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"grade": "V5"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "hobby.sport_climb_boulder_convert",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
This bouldering grade conversion calculator accepts a single grade token, auto-detects whether it is V-scale or Fontainebleau (or honors an explicit from_scale), and returns both labels from a fixed consensus table covering VB and V0 through V17 plus Font grades from 3 through 9A. Unknown tokens fail with invalid_input instead of inventing a made-up equivalence. The free browser tool and the paid API share one pure deterministic module, so training logs, trip planners, and bulk guide importers never disagree on the same grade string.
Input contract, accepted grade forms, and response shape
V-scale inputs may be VB, V0 through V17, with optional spacing or a lowercase v; V0+ is treated as V0 on this table. Fontainebleau inputs may be 3, 4, 4+, 5, 5+, or lettered bands from 6A through 9A with an optional plus, case-insensitive, with optional Font or FB prefixes. Classic checks include V5 converting to 6C, 7A converting to V6, and V10 converting to 7C+. Wire the free browser form when packing for a single trip, then call the identical contract from scripts when you import a guidebook CSV or normalize gym setters’ notes. Send a JSON body with the required field grade, or one of its aliases input_grade, value, or boulder_grade. An optional from_scale field forces interpretation when you already know the source ladder: use v_scale (aliases v, hueco, usa) or fontainebleau (aliases font, fb, bleau). When from_scale is omitted or set to auto, tokens that start with V are parsed as V-scale and everything else as Fontainebleau, with a small rule that bare integers 3–5 prefer Font because those are common outdoor labels. Missing fields, empty strings, unsupported numbers such as V20 or Font 10, and non-grade junk fail with invalid_input and are not billed. On success the response echoes grade_input, reports from_scale as the ladder that was used, returns v_scale and fontainebleau (plus font as a short alias of the Font label), includes numeric v_rank and font_rank for sorting, names the table bouldering_v_font_consensus, and provides formula, note, and message strings suitable for UI copy. Successful API calls use the published base price of $0.002 per item; validation failures do not consume prepaid balance.
Technical questions
What does the bouldering grade conversion calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.