Table of Contents

Toggle## What is a bilateral tolerance?

A bilateral tolerance is a plus or minus tolerance (+/-). It allows variation from the nominal size in both a positive and negative direction.

In most cases, the bilateral tolerance will be specified as equal in both directions such as 10.0mm +/- 0.5mm.

This is not always the case though and a bilateral tolerance does not need to have equal positive and negative tolerances. 10.0mm +0.2mm/-0.3mm would be an acceptable bilateral tolerance as well.

Here are some quick bilateral tolerance examples:

- 5.5″ +/- 0.25″
- 5.5″ +1.0″/-0.5″
- 25.5mm +0.1mm/-0.2mm
- 30.6mm +/- 0.3mm

Notice that in each of the examples there is allowed variation (tolerance) from the nominal size in both directions.

A tolerance of 25.5mm +0/-0.2mm would not be a bilateral tolerance because it has no tolerance in the positive direction. This would be an example of a unilateral tolerance.

## Bilateral tolerance symbol

There is no GD&T symbol for a bilateral tolerance.

Per ASME Y14.5, the notation for a bilateral tolerance is to show a plus and a minus tolerance associated with a nominal dimension and neither of them is a zero.

Want to learn how to type GD&T symbols with** no special fonts needed?**

## How to read a bilateral tolerance

Let’s start with our examples from above

- 5.5″ +/- 0.25″
- 5.5″ +1.0″/-0.5″
- 25.5mm +0.1mm/-0.2mm
- 30.6mm +/- 0.3mm

Now let’s break it down so you can see what the nominal size is as well as the top and bottom ends of the tolerance zone.

Nominal Size | Bottom of Tolerance | Top of Tolerance |

5.5" | 5.25" | 5.75" |

5.5" | 5.0" | 6.5" |

25.5mm | 25.3mm | 25.6mm |

30.6mm | 30.3mm | 30.9mm |

## Bilateral tolerance examples

## Types of bilateral tolerances

### Equal bilateral tolerance

An equal bilateral tolerance will have equal plus and minus tolerances such as 6.35 +/- 0.025 as shown in the example above.

### Unequal bilateral tolerance

An unequal bilateral tolerance will have plus and minus tolerances that are not the same and neither is zero such as 17.0 +0.1/-0.2 as shown in the example above.

## Bilateral tolerances compared to other tolerance types

### Bilateral tolerance vs unilateral tolerance

A bilateral tolerance allows a tolerance in both directions.

A unilateral tolerance allows a tolerance in only one direction.

A bilateral tolerance is plus ** AND **minus tolerance. A unilateral tolerance is a plus

**minus tolerance.**

__OR__Here are some examples of unilateral tolerances:

- 10.0mm +0/+0.5mm
- 5.515″ +0.010″/+0.015″
- 2.325″ +0/-0.005″
- 4.5mm -0.2/-0.3mm

### Bilateral tolerance vs limit tolerance

A bilateral tolerance specifies a nominal size and a plus/minus tolerance. These values are used to determine the tolerance range for a feature.

A limit tolerance skips the calculation step and simply gives you the tolerance range.

The table below shows bilateral tolerances with their equivalent limit tolerances.

Bilateral Tolerance | Limit Tolerance |

10.0 +/-0.5 | 9.5 - 10.5 |

5.525 +0.025/-0.050 | 5.475 - 5.550 |

7.55 +/+0.15 | 7.40 - 7.70 |

2.324 +0.005/-0.010 | 2.314 - 2.329 |

## Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And **MachinistGuides.com readers get an exclusive discount on training!**

## Related articles

For more information see these related articles: