---
title: "First-In-First-Out | Intro to Industrial Engineering"
description: "First-in-first-out (FIFO) is an inventory method where the oldest items are used or sold first, helping Industrial Engineering reduce waste and track costs."
canonical: "https://fiveable.me/introduction-industrial-engineering/key-terms/first-in-first-out"
type: "key-term"
subject: "Intro to Industrial Engineering"
unit: "Unit 3"
---

# First-In-First-Out | Intro to Industrial Engineering

## Definition

First-in-first-out (FIFO) is an inventory rule where the oldest goods move out of the system first. In Intro to Industrial Engineering, it shows up in inventory flow, production, and service systems where order matters.

## What It Is

First-in-first-out, or FIFO, is a way of moving materials through a system so the oldest item gets used, sold, or processed before newer ones. In Intro to Industrial Engineering, that usually means you are thinking about inventory flow, work-in-process, or service queues as a controlled sequence instead of a random pile of items.

The basic idea is simple: whatever enters the system first should leave first. In a warehouse, that might mean pallets with the earliest receipt date are picked before newer stock. In a manufacturing line, parts can be issued in the order they arrived so older materials do not sit around and get damaged, outdated, or forgotten.

FIFO matters because industrial systems are not just about making things, they are about moving things efficiently. If you let new items jump ahead of older ones, you can create waste, spoilage, and messy inventory records. FIFO gives the process a clear rule, which makes it easier to plan storage space, shelf rotation, and production flow.

A big reason Industrial Engineering uses FIFO is that it supports lean thinking. When materials move in a consistent order, you can see problems more clearly, like slow stations, excess stock, or items waiting too long. It also fits well with perishable goods, where the oldest food, chemicals, or medical supplies should be used first to avoid expiration.

FIFO is not just a storage rule. It can describe how jobs, patients, parts, or orders are handled in a queue. For example, if a service desk serves customers in the order they arrive, that is FIFO behavior. If a system changes the order, then your waiting times, fairness, and throughput can change too. That is why industrial engineers pay attention to whether FIFO is actually being followed or whether the real process is quietly using a different rule.

## Why It Matters

FIFO shows up anywhere an Intro to Industrial Engineering class talks about process flow, inventory management, or service systems. It gives you a clean way to describe how items move through a system and whether that movement is efficient or wasteful.

This term also connects to cost and quality decisions. If older inventory is used first, businesses are less likely to lose money to spoilage, obsolescence, or expired stock. That means FIFO can affect both the physical performance of a system and the financial picture that comes out of it.

You will also see FIFO when comparing different ways to run a system. A line that follows FIFO may be fair and easy to track, but it can create longer waits for some jobs if a bottleneck slows the whole sequence. That makes FIFO a useful reference point when your class discusses tradeoffs between smooth flow, storage limits, and customer service.

In manufacturing and supply chain settings, FIFO is a simple rule that supports more advanced analysis. Once you know the sequence of items, you can start asking better questions about inventory turnover, backlog, and where the process gets stuck. It is one of those terms that looks small, but it helps organize a lot of the course.

## Connections

### Inventory Management

FIFO is one rule inside inventory management. When you track stock levels, reorder points, and item age, FIFO helps decide which units leave the shelf first. That matters when the class looks at storage costs, expiration risk, or how to keep records accurate across repeated shipments.

### Perishable Goods

Perishable goods are the clearest place where FIFO makes sense. Food, medicine, and other time-sensitive items can lose value fast, so the oldest stock should move out before it spoils. Industrial Engineering uses FIFO here to reduce waste and keep the process aligned with shelf life.

### Supply Chain Management

FIFO affects how products move through the supply chain from receiving to storage to shipment. If incoming stock is not organized by age, the system can send out newer items while older ones sit too long. That creates waste, higher holding costs, and possible service problems downstream.

### [last-in-first-out](/introduction-industrial-engineering/key-terms/last-in-first-out)

last-in-first-out is the opposite order rule, where the newest item moves first. Comparing it with FIFO helps you see why process design matters: the same inventory can lead to very different outcomes depending on the flow rule. In class, this comparison often comes up when analyzing storage, fairness, or cost.

## On the AP Exam

A quiz question might give you a warehouse or service scenario and ask which inventory rule is being used. You should look for the phrase that the oldest items are processed first, then identify that as FIFO. If the question includes spoilage, expiration dates, or stock rotation, FIFO is usually the best match.

In a problem set or case analysis, you may need to explain how FIFO changes waste, inventory value, or waiting behavior. A strong answer connects the rule to the outcome, such as fewer expired goods, cleaner stock records, or a more orderly queue. If the scenario asks whether a process is efficient, you can also mention that FIFO makes flow easier to track but can still reveal bottlenecks when one step slows everything down.

## first-in-first-out vs last-in-first-out

These are easy to mix up because both describe the order items leave a system. FIFO means the oldest item leaves first, while last-in-first-out means the newest item leaves first. In Industrial Engineering, FIFO is common for perishables and flow control, while last-in-first-out can change inventory age, cost, and waiting patterns in very different ways.

## Key Takeaways

- First-in-first-out means the oldest item enters service, inventory, or processing first.
- In Industrial Engineering, FIFO is used to keep inventory moving in a clear order and reduce waste from spoilage or aging stock.
- FIFO is useful in both manufacturing and service systems, especially when sequence affects cost, fairness, or quality.
- The term is not just about storage, it also describes how jobs or customers move through a queue.
- If a problem mentions older items being used before newer ones, FIFO is usually the rule you want.

## FAQs

### What is first-in-first-out in Intro to Industrial Engineering?

First-in-first-out, or FIFO, is a rule where the oldest inventory item, job, or order is handled before newer ones. In Industrial Engineering, it is used to keep flow organized, reduce waste, and make system timing easier to track. You will see it in warehouses, production lines, and service queues.

### How does FIFO work in inventory management?

FIFO means the first items received are the first ones used or shipped. That keeps older stock from sitting too long and helps prevent spoilage, obsolescence, or inaccurate inventory value. It is a simple rotation rule that supports cleaner records and better material flow.

### Is FIFO the same as last-in-first-out?

No. FIFO uses the oldest item first, while last-in-first-out uses the newest item first. They can lead to very different results for waste, storage, and waiting time, so it is worth checking the wording carefully on homework or quiz questions.

### Why do industrial engineers care about FIFO?

Industrial engineers care about FIFO because it affects how smoothly a system runs. It can reduce waste in perishable inventory, make queues easier to manage, and help reveal bottlenecks when one step slows the whole process. That makes it a practical rule for both analysis and operations.

## Related Study Guides

- [3.3 Applications in Service and Manufacturing Industries](/introduction-industrial-engineering/unit-3/applications-service-manufacturing-industries/study-guide/A0OAwLNnAXQ7ytRp)

## About This Document

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- [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing
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