# Inches of mercury to Hectopascals (inHg to hPa)

> Convert inches of mercury to hectopascals: 1 inHg = 33.8639 hPa. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

- Page id: `inhg-to-hpa` · Quantity: Pressure (`pressure`, base unit Pa) · Tool: `convert_units`
- Canonical page: https://tttkmbb.com/conversion/inhg-to-hpa · This document: https://tttkmbb.com/conversion/inhg-to-hpa.md · JSON: https://tttkmbb.com/conversion/inhg-to-hpa.json (add `?value=` for a result)

## Formula

- `1 inHg = 33.8639 hPa`
- `hectopascals = inches of mercury × 33.8638864`
- Reverse: `inches of mercury = hectopascals × 0.0295299833`

The factor follows from the SI definitions of both units (NIST SP 811); values below are rounded to 6 significant figures, the API returns up to 12.

## Worked examples

- 5 inHg = 169.319 hPa
- 12.5 inHg = 423.299 hPa
- 100 inHg = 3386.39 hPa

## Conversion table

| Inches of mercury (inHg) | Hectopascals (hPa) |
| --- | --- |
| 1 | 33.8639 |
| 2 | 67.7278 |
| 3 | 101.592 |
| 4 | 135.456 |
| 5 | 169.319 |
| 6 | 203.183 |
| 7 | 237.047 |
| 8 | 270.911 |
| 9 | 304.775 |
| 10 | 338.639 |
| 15 | 507.958 |
| 20 | 677.278 |
| 25 | 846.597 |
| 30 | 1015.92 |
| 40 | 1354.56 |
| 50 | 1693.19 |
| 75 | 2539.79 |
| 100 | 3386.39 |
| 200 | 6772.78 |
| 250 | 8465.97 |
| 500 | 16931.9 |
| 1000 | 33863.9 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=inHg&to_unit=hPa` → unified JSON envelope with `result.values.result`, `formula`, `factor`, `sources`, `freshness`
- MCP: server `https://tttkmbb.com/mcp`, tool `convert_units` with `{"value":5,"from_unit":"inHg","to_unit":"hPa"}`
- All pressure units: https://tttkmbb.com/api/v1/units?quantity=pressure · full converter: [Pressure Converter](https://tttkmbb.com/conversion/pressure.md)
- Authentication: none. Freshness: `static` (fixed conversion factors).

## FAQ

**How many hectopascals are in one inch of mercury?**

1 inHg = 33.8639 hPa. The factor comes from the SI definitions of both units (NIST SP 811 / BIPM), so it is exact or correct to at least 10 significant figures.

**What is the formula to convert inches of mercury to hectopascals?**

Multiply the value in inches of mercury by 33.8638864: hectopascals = inches of mercury × 33.8638864. For example, 5 inHg = 169.319 hPa.

**How do I convert hectopascals back to inches of mercury?**

Multiply by the inverse factor 0.0295299833 (inches of mercury = hectopascals × 0.0295299833), or use the hectopascals-to-inches of mercury page.

## Related conversions

- [Hectopascals to inches of mercury](https://tttkmbb.com/conversion/hpa-to-inhg.md) (reverse)
- [Psi to Bar](https://tttkmbb.com/conversion/psi-to-bar.md)
- [Bar to Psi](https://tttkmbb.com/conversion/bar-to-psi.md)
- [Psi to Kilopascals](https://tttkmbb.com/conversion/psi-to-kpa.md)
- [Kilopascals to Psi](https://tttkmbb.com/conversion/kpa-to-psi.md)
- [Bar to Kilopascals](https://tttkmbb.com/conversion/bar-to-kpa.md)
- [Kilopascals to Bar](https://tttkmbb.com/conversion/kpa-to-bar.md)
- [Atmospheres to Pascals](https://tttkmbb.com/conversion/atm-to-pa.md)
- [Pascals to Atmospheres](https://tttkmbb.com/conversion/pa-to-atm.md)

## Data Sources

- NIST Special Publication 811 – Guide for the Use of the International System of Units (SI), Appendix B conversion factors — https://www.nist.gov/pml/special-publication-811 (standard, retrieved 2026-09-24)
- BIPM – The International System of Units (SI Brochure, 9th edition) — https://www.bipm.org/en/publications/si-brochure (standard, retrieved 2026-09-24)
- Wikipedia – Conversion of units — https://en.wikipedia.org/wiki/Conversion_of_units (reference, retrieved 2026-09-24)