# Bicycle Frame Size Calculator

> Bicycle Frame Size Calculator is a paid API for AI agents from bike-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-30).

Estimates bicycle frame size (seat tube in cm and S/M/L letter size) from inseam measurement and bike type, with an optional height-based letter size cross-check.

## Facts

- Endpoint: GET https://bike-calc.x402tookit.com/frame-size?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/bicycle-frame-size-calculator-19ca4455
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_7tz9hl2CEOYR9Gd_M4WI8

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability bicycle-frame-size-calculator-19ca4455
```

Example prompt: I have an inseam of 81 cm and I'm shopping for a road bike — what frame size should I be looking at, and what's my S/M/L size if I also give you my height of 178 cm?

## When to prefer this

Use this endpoint when you need a quick, formula-based starting frame size estimate from inseam and bike type, especially when the user does not yet have a specific bike in mind and wants a cm seat tube length plus letter size. It covers road, road-compact, gravel, mountain, hybrid, and city bike types. Prefer this over a full bike fitting service when no professional fit data is available and a rough estimate is sufficient.

## Known failure modes

- Missing required inseam parameter returns a 400 error
- Inseam value outside plausible human range may return degraded or null results
- Invalid bikeType string falls back to default road calculation
- Providing height without inseam still requires inseam as it is required
- Unit mismatch (e.g. passing inches without unit=in) yields incorrect frame size

## How this service works

Rough bike frame size (seat tube cm and S/M/L) from inseam by bike type, with a height-based letter size cross-check.

## Output

Returns the estimated seat tube length in cm (and inches), the nearest even cm size, adjacent sizes for comparison, the S/M/L letter size derived from inseam, an optional letter size cross-check from body height, the bike type used, and a disclaimer about the estimates being a starting point rather than a definitive fit.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "inseam"
     ],
     "properties": {
      "unit": {
       "type": "string",
       "description": "cm (default) or in"
      },
      "inseam": {
       "type": "number",
       "description": "Inseam in cm (or inches with unit=in)"
      },
      "bikeType": {
       "type": "string",
       "description": "road, road-compact, gravel, mountain, hybrid, city (default road)"
      },
      "heightCm": {
       "type": "number",
       "description": "Body height in cm, for the S/M/L cross-check"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "factor": {
       "type": [
        "null",
        "number"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "bikeType": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "heightCm": {
       "type": [
        "null",
        "number"
       ]
      },
      "inseamCm": {
       "type": [
        "null",
        "number"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "seatTubeCm": {
       "type": [
        "null",
        "number"
       ]
      },
      "nearestEvenCm": {
       "type": [
        "nul
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/bicycle-frame-size-calculator-19ca4455/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from bike-calc.x402tookit.com](https://www.zero.xyz/host/bike-calc.x402tookit.com/llms.txt)