# Pressure Converter

> Converts pressure between pascals (Pa to MPa), bar/millibar, standard atmospheres, psi and ksi, millimetres and inches of mercury, torr and technical atmospheres (kgf/cm²) using NIST factors (1 psi = 6894.757293168 Pa, 1 atm = 101325 Pa).

- Calculator id: `pressure` · Category: Unit Conversion (`conversion`) · Tool name: `convert_pressure`
- Canonical page: https://tttkmbb.com/conversion/pressure · This document: https://tttkmbb.com/conversion/pressure.md · JSON definition: https://tttkmbb.com/conversion/pressure.json

## Purpose

Converts pressure between pascals (Pa to MPa), bar/millibar, standard atmospheres, psi and ksi, millimetres and inches of mercury, torr and technical atmospheres (kgf/cm²) using NIST factors (1 psi = 6894.757293168 Pa, 1 atm = 101325 Pa).

**Use when:** You need tyre, weather, hydraulic, vacuum or blood pressure in another unit, e.g. psi to bar, atm to kPa or mmHg to kPa.

**Do not use when:** You need to compute pressure from force and area (a physics calculation, not a unit conversion) or the gas law relation between pressure, volume and temperature (use ideal-gas-law).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `value` | number |  | required | Amount to convert, expressed in from_unit. |
| `from_unit` | enum: Pa \| hPa \| kPa \| MPa \| bar \| mbar \| atm \| psi \| ksi \| mmHg \| torr \| inHg \| kgf/cm2 |  | required | Unit of the input value. Accepted symbols: Pa, hPa, kPa, MPa, bar, mbar, atm, psi, ksi, mmHg, torr, inHg, kgf/cm2; spelled-out names and common abbreviations are accepted too. |
| `to_unit` | enum: Pa \| hPa \| kPa \| MPa \| bar \| mbar \| atm \| psi \| ksi \| mmHg \| torr \| inHg \| kgf/cm2 |  | required | Unit to convert into (same symbols as from_unit). |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `result` | number |  | Converted value expressed in to_unit (rounded to 6 decimals; see result_text for very small or very large values). |
| `result_text` | string |  | The conversion as text with 6 significant figures, e.g. "5 mi = 8.04672 km". |
| `formula` | string |  | Relation used, e.g. "1 mi = 1.609344 km". |
| `factor` | number |  | Multiplier from from_unit to to_unit (result = value × factor); absent for non-linear conversions. |
| `conversion_table` | object |  | The input value expressed in every supported pressure unit (6 significant figures), keyed by unit symbol. |

## Formula

`result = value × factor, factor = (1 from_unit in Pa) / (1 to_unit in Pa)`

mmHg uses the conventional value 133.322387415 Pa (mercury density 13.5951 g/cm³ at 0 °C); torr is defined as exactly 1/760 atm, so 1 mmHg ≈ 1.000000142 torr. inHg = 25.4 mmHg.

## 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 2026-09-23)
- BIPM – The International System of Units (SI Brochure, 9th edition) — https://www.bipm.org/en/publications/si-brochure (standard, retrieved 2026-09-23)
- Wikipedia – Conversion of units — https://en.wikipedia.org/wiki/Conversion_of_units (reference, retrieved 2026-09-23)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/pressure?value=…&from_unit=…&to_unit=…`
- `POST https://tttkmbb.com/api/v1/calculate/pressure` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/pressure · OpenAPI operationId `convert_pressure` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "pressure", "inputs": {…}}`

## Example

- 1 atm to psi: inputs `{"value":1,"from_unit":"atm","to_unit":"psi"}` → `{"result":14.695949,"formula":"1 atm = 14.69594878 psi","conversion_table":{"bar":1.01325,"mmHg":760,"kPa":101.325,"torr":760}}`
- 32 psi to bar: inputs `{"value":32,"from_unit":"psi","to_unit":"bar"}` → `{"result":2.206322,"conversion_table":{"kPa":220.632,"atm":2.17747}}`

```
GET https://tttkmbb.com/api/v1/calculate/pressure?value=1&from_unit=atm&to_unit=psi
```

## Limitations

You need to compute pressure from force and area (a physics calculation, not a unit conversion) or the gas law relation between pressure, volume and temperature (use ideal-gas-law). mmHg uses the conventional value 133.322387415 Pa (mercury density 13.5951 g/cm³ at 0 °C); torr is defined as exactly 1/760 atm, so 1 mmHg ≈ 1.000000142 torr. inHg = 25.4 mmHg. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Is bar the same as atmosphere?**

No. 1 bar = 100,000 Pa exactly; 1 atm = 101,325 Pa = 1.01325 bar = 14.6959 psi.

**Gauge or absolute pressure?**

The converter changes units only. Tyre gauges read pressure above atmospheric (psig); add 1 atm (14.6959 psi) for absolute pressure.

## Related

- [Force Converter](https://tttkmbb.com/conversion/force.md) — Convert the force units behind psi and kgf/cm².
- [Ideal Gas Law Calculator](https://tttkmbb.com/chemistry/ideal-gas-law.md) — Pressure–volume–temperature of a gas.
- [Density Converter](https://tttkmbb.com/conversion/density.md) — Hydrostatic pressure needs fluid density.