---
title: "Loss factor — Class A Atlas glossary"
description: "The percentage difference between rentable and usable square feet."
canonical: https://classa.info/glossary/loss-factor
pageType: glossary
lastUpdated: 2026-04-01T00:00:00.000Z
license: "CC BY 4.0 with attribution to Class A Atlas (https://classa.info)."
---

> The percentage difference between rentable and usable square feet.

## TL;DR

- The percentage difference between rentable and usable square feet.
- Also called add-on factor or core factor.

# Loss factor

*Measurement · US, Global*

## Short definition

The percentage difference between rentable and usable square feet.

## Full definition

Also called add-on factor or core factor. A 25% loss factor means the tenant pays rent on 25% more area than they can use. Loss factors vary materially: trophy Manhattan often runs 28-32%; modern London [Class A](/glossary/class-a) around 12-15%; Singapore Grade A around 10-15%. A 5% difference in loss factor is real money.

## Example

A 30,000 RSF floor with 25% loss factor = 22,500 USF.

## Why this matters for Class A leasing

Loss factor is part of the measurement vocabulary that institutional Class A occupiers, landlords, and advisers use across US, Global markets. Understanding it correctly affects how you read lease documents, model occupancy economics, and benchmark deal terms across cities. Class A Atlas tracks regional variation alongside the global standard so [cross-border](/topics/cross-border-expansion) occupiers can translate quickly.

## See also

- [Rentable square feet (RSF)](/glossary/rentable-square-feet)
- [Usable square feet (USF)](/glossary/usable-square-feet)
- [BOMA standard](/glossary/boma)

## Related guides

- [How to choose a Class A office: a working framework](/guides/how-to-choose-class-a-office)

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Citation: Source: Class A Atlas (https://classa.info/glossary/loss-factor), updated 2026-04-01T00:00:00.000Z.