# Hectopascals to Inches of mercury (hPa to inHg)

> Convert hectopascals to inches of mercury: 1 hPa = 0.02953 inHg. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

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

## Formula

- `1 hPa = 0.02953 inHg`
- `inches of mercury = hectopascals × 0.0295299833`
- Reverse: `hectopascals = inches of mercury × 33.8638864`

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 hPa = 0.14765 inHg
- 12.5 hPa = 0.369125 inHg
- 100 hPa = 2.953 inHg

## Conversion table

| Hectopascals (hPa) | Inches of mercury (inHg) |
| --- | --- |
| 1 | 0.02953 |
| 2 | 0.05906 |
| 3 | 0.0885899 |
| 4 | 0.11812 |
| 5 | 0.14765 |
| 6 | 0.17718 |
| 7 | 0.20671 |
| 8 | 0.23624 |
| 9 | 0.26577 |
| 10 | 0.2953 |
| 15 | 0.44295 |
| 20 | 0.5906 |
| 25 | 0.73825 |
| 30 | 0.885899 |
| 40 | 1.1812 |
| 50 | 1.4765 |
| 75 | 2.21475 |
| 100 | 2.953 |
| 200 | 5.906 |
| 250 | 7.3825 |
| 500 | 14.765 |
| 1000 | 29.53 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=hPa&to_unit=inHg` → 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":"hPa","to_unit":"inHg"}`
- 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 inches of mercury are in one hectopascal?**

1 hPa = 0.02953 inHg. 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 hectopascals to inches of mercury?**

Multiply the value in hectopascals by 0.0295299833: inches of mercury = hectopascals × 0.0295299833. For example, 5 hPa = 0.14765 inHg.

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

Multiply by the inverse factor 33.8638864 (hectopascals = inches of mercury × 33.8638864), or use the inches of mercury-to-hectopascals page.

## Related conversions

- [Inches of mercury to hectopascals](https://tttkmbb.com/conversion/inhg-to-hpa.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)