For free accounts, Google Analytics allows 5 calculated metrics per view. These are custom equations to assist insights. For many great ideas of custom calculated metrics, read this article.

Note for creating custom calculated metrics

Float: A number with decimals
Integer: A whole number
Currency (Decimal): Monetary number with decimals
Time: Duration (Send data in seconds)
Percent: Percentage value

Example calculated metrics using Nebula custom metrics

Avg. Max Scroll Percent (Percent)
Requires “Max Scroll Percent” custom metric (Nebula Options). Custom Report should have this metric along with “Unique Pageviews” against dimensions “Page”, “Source / Medium”.
{{Max Scroll Percent}} / (100*{{Unique Pageviews}})

Form Impressions / Page (Percent)
Requires “Form Impressions” custom metric (Nebula Options). Custom Report should have this metric along with “Unique Pageviews” against dimensions “Page”, “Source / Medium”, and/or “Form Impressions”.
{{Form Impressions}} / {{Unique Pageviews}}

Avg. Page Visible Time / Page (Time)
Useful for page reporting. Requires “Page Visible Time” custom metric (Nebula Options). Custom Report should have this metric along with “Unique Pageviews” against dimension “Page”.
{{Page Visible Time}} / {{Unique Pageviews}}

Avg. Page Visible Time / Session (Time)
Useful for acquisition reporting. Requires “Page Visible Time” custom metric (Nebula Options). Custom Report should have this metric along with “Unique Pageviews” against dimension “Source / Medium”.
{{Page Visible Time}} / {{Sessions}}

Additional example calculated metrics (some using Nebula custom dimensions)

Non-Bounced Pageviews (Integer)
{{Pageviews}} - {{Bounces}}

Average Pages per User (Float)
{{Pageviews}} / {{Users}}

Downloads per User (Float)
{{Notable Downloads}} / {{Users}}

Form Completion Rate (Percentage)
{{Notable FormSubmissions}} / {{Notable Form Views}}

AdWords Cost per Session (Currency)
{{Cost}} / {{Sessions}}

Video Completion Rate (Percentage)
{{Video Completions}} / {{Video Starts}}

Average Video Play Time (Float)
{{Video Play Time}} / {{Sessions}}

AdWords Cost per Video Play (Currency)
{{Cost}} / {{Video Starts}}

See built-in Nebula custom metrics to come up with additional calculated metrics, or report your own custom metrics for further evaluation.