# Atmospheres to Bar (atm to bar)

> Convert atmospheres to bar: 1 atm = 1.01325 bar. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

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

## Formula

- `1 atm = 1.01325 bar`
- `bar = atmospheres × 1.01325`
- Reverse: `atmospheres = bar × 0.9869232667`

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 atm = 5.06625 bar
- 12.5 atm = 12.6656 bar
- 100 atm = 101.325 bar

## Conversion table

| Atmospheres (atm) | Bar (bar) |
| --- | --- |
| 1 | 1.01325 |
| 2 | 2.0265 |
| 3 | 3.03975 |
| 4 | 4.053 |
| 5 | 5.06625 |
| 6 | 6.0795 |
| 7 | 7.09275 |
| 8 | 8.106 |
| 9 | 9.11925 |
| 10 | 10.1325 |
| 15 | 15.1988 |
| 20 | 20.265 |
| 25 | 25.3313 |
| 30 | 30.3975 |
| 40 | 40.53 |
| 50 | 50.6625 |
| 75 | 75.9938 |
| 100 | 101.325 |
| 200 | 202.65 |
| 250 | 253.313 |
| 500 | 506.625 |
| 1000 | 1013.25 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=atm&to_unit=bar` → 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":"atm","to_unit":"bar"}`
- 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 bar are in one atmosphere?**

1 atm = 1.01325 bar. 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 atmospheres to bar?**

Multiply the value in atmospheres by 1.01325: bar = atmospheres × 1.01325. For example, 5 atm = 5.06625 bar.

**How do I convert bar back to atmospheres?**

Multiply by the inverse factor 0.9869232667 (atmospheres = bar × 0.9869232667), or use the bar-to-atmospheres page.

## Related conversions

- [Bar to atmospheres](https://tttkmbb.com/conversion/bar-to-atm.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)