1. Open Rate

This is the percentage of all people who received the email who opened it.

Formula:

Open Rate = (Total Opens ÷ Total Delivered) × 100

So if you sent a campaign to 100 people and 47 opened it, you’d get your 47.4% open rate.

2. Click Rate

This is the percentage of all people who received the email who clicked at least one link.

Formula:

Click Rate = (Total Unique Clickers ÷ Total Delivered) × 100

In your example:

42.1% of everyone you sent the email to clicked something inside it.

That’s exceptionally high.

3. Click-to-Open Rate (CTOR)

This is the percentage of people who opened the email who then clicked a link.

Formula:

CTOR = (Total Unique Clickers ÷ Total Opens) × 100

And here’s the key:

Why the Click-to-Open Rate can be bigger than the Open Rate

Because they’re measuring totally different groups:

• Open Rate looks at everyone who received the email.
• Click-to-Open looks only at people who opened it.

If almost everyone who opened the email clicked something, your CTOR will be very high — even higher than your click rate, and even larger than half your open rate.

Let’s do the math with these numbers to show how it works:

• 47.4% opened
• 42.1% clicked
• CTOR = 42.1 ÷ 47.4 ≈ 88.9%

Meaning: Nearly 9 out of 10 people who opened your email clicked.That’s excellent engagement.

4. A quick analogy

• Open Rate = “How many people walked into the store?”
• Click Rate = “How many people bought something compared to all passersby?”
• Click-to-Open = “Of the people who walked in, how many bought something?”

You can have relatively few people walk in, but if most who do walk in make a purchase, your conversion rate (CTOR) can be very high.