Rates & Unit Rates

Why This Matters for Nursing: IV drip rates (mL per hour), medication dosing (mg per kg), and vital signs (beats per minute) are all rates. Understanding unit rates helps you calculate exactly what each patient needs.

What You Need to Know

A rate is a ratio that compares two quantities with DIFFERENT units: - 60 miles per 2 hours - $15 for 3 items - 120 mL in 4 hours

A unit rate expresses how much of one thing per ONE unit of another: - 30 miles per 1 hour (30 mph) - $5 per 1 item - 30 mL per 1 hour

🧠 Memory Trick

"Per" means DIVIDE

"Miles per hour" = miles ÷ hours "Price per item" = price ÷ items

To find a unit rate, divide to get "per 1"

Finding Unit Rates

Method:

Divide the first quantity by the second quantity

Example: 240 miles in 4 hours

Unit rate = 240 miles ÷ 4 hours = 60 miles per hour

Using Unit Rates

Once you have a unit rate, multiply to find any amount:

If a car travels 60 mph, how far in 7 hours? - 60 miles/hour × 7 hours = 420 miles

✏️ Worked Examples

Example 1: Finding Unit Rate

Problem: A 500 mL IV bag runs over 4 hours. What's the rate in mL per hour?

Step 1 — Identify what "per hour" means. A unit rate always tells you the amount "per 1" of something. Here we want mL per 1 hour.

Step 2 — Divide the total by the number of units. 500 mL ÷ 4 hours = 125 mL/hour.

Answer: 125 mL per hour

💡 "Per" always tells you to divide. mL per hour = mL ÷ hours. If you get confused, just remember: the word "per" means ÷.