---
title: "Unilateral and bilateral tolerance conversion"
subject: "Metrology"
chapter: 9
key: "semester_3/metrology:unilateral-bilateral-tolerance"
source: https://www.bctengineer.com/q/semester_3/metrology/unilateral-bilateral-tolerance
site: BCT Engineering
---

# Unilateral and bilateral tolerance conversion

Metrology · Chapter 9: Limits, Fits and Tolerance

- Asked in: year not given, 5 marks
- Video: [Unilateral to bilateral Tolerance / Bilateral to unilateral Tolerance coversion, how to and Why](https://www.youtube.com/watch?v=Ucz9kayrI4M) — shrikrishi
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/metrology/unilateral-bilateral-tolerance
- Whole chapter: https://www.bctengineer.com/md/semester_3/metrology/chapter-9

## Question

Differentiate between unilateral and bilateral tolerance with examples and state when each is used. Convert the bilateral dimension $40.00 \pm 0.03$ mm into a unilateral form with the same limits, and state the type of tolerance in $60^{+0.05}_{+0.02}$ mm.

## Short answer

Unilateral tolerance has variation on one side of basic size (e.g., 25+0.03/0); bilateral on both sides (e.g., 25±0.02). Limits of 40.00±0.03 are 39.97 and 40.03, so unilateral form is 39.97+0.06/0. The dimension 60+0.05+0.02 gives limits 60.02 and 60.05; it is unilateral with tolerance 0.03 mm.

## Answer

| Point | Unilateral | Bilateral |
|---|---|---|
| Definition | Tolerance on one side of the basic size only | Tolerance on both sides of the basic size |
| Example | $25^{+0.03}_{0}$ or $25^{0}_{-0.02}$ | $25 \pm 0.02$ or $25^{+0.03}_{-0.01}$ |
| Basic size | One of the limits | Lies between the limits |
| Use | Interchangeable parts, hole and shaft systems (the basic size is the datum of fits); allows fixed tools to be used and the tolerance to be changed without changing the datum | Where variation on either side is acceptable, e.g. positions of holes, centre distances, and in machining and assembly dimensions |
| Gauging | Easier to adjust setting and to change tolerance | Symmetrical; the setting at the mean size |

**Conversion:** the limits of $40.00 \pm 0.03$ are $39.97$ and $40.03$ mm; the total tolerance is $0.06$ mm. As a unilateral dimension with the same limits:

$$
39.97^{+0.06}_{\ 0}\ \text{mm}
$$

**Type of $60^{+0.05}_{+0.02}$:** both deviations are positive, so the limits are $60.02$ and $60.05$ mm and the basic size 60 mm lies outside the tolerance zone. It is a unilateral tolerance (both limits are on the same side of the basic size), with a tolerance of $0.05 - 0.02 = 0.03$ mm.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is a unilateral tolerance?
   A. Tolerance equal on both sides of the basic size
   B. Tolerance on one side of the basic size only
   C. Tolerance given only for the shaft
   D. Tolerance with a zero total width
   Answer: B. A unilateral tolerance lies wholly on one side of the basic size, as in 25 +0.03/0. (Key point: Unilateral tolerance)

2. The bilateral dimension 40.00 +/- 0.03 mm is written unilaterally with the same limits as:
   A. 39.97 +0.06 / 0 mm
   B. 40.03 +0.06 / 0 mm
   C. 40.00 +0.03 / 0 mm
   D. 39.97 +0.03 / 0 mm
   Answer: A. Limits are 39.97 and 40.03, total tolerance 0.06, so basic size 39.97 with +0.06 and 0. (Key point: Conversion)

3. What is the tolerance type and its value for 60 (+0.05, +0.02) mm?
   A. Bilateral, 0.07 mm
   B. Bilateral, 0.03 mm
   C. Unilateral, 0.03 mm
   D. Unilateral, 0.05 mm
   Answer: C. Both deviations are positive so both limits (60.02 and 60.05) lie on the same side of 60; tolerance is 0.05 - 0.02 = 0.03 mm. (Key point: Type of 60 +0.05/+0.02)

## Related in Metrology

- [Limits of a 40 H7/g6 hole-shaft fit](https://www.bctengineer.com/question.md?key=semester_3%2Fmetrology%3Afit-40-h7-g6-calculation) — Metrology, chapter 9
- [Basic terms of limits, fits and tolerances](https://www.bctengineer.com/question.md?key=semester_3%2Fmetrology%3Alimits-fits-terminology) — Metrology, chapter 9
- [Classify fits from given limits of size](https://www.bctengineer.com/question.md?key=semester_3%2Fmetrology%3Aclassify-fits-from-limits) — Metrology, chapter 9

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