About this block

Which Size To Buy sets the Field Pack 20 and the Field Pack 30 in two spec columns, each with capacity, weight, laptop fit, and the honest underseat line, then a "Built for" note and a plain verdict. The 20 admits it is "the bag most people mean when they say our name," and the 30 warns "carried half full, it slouches and you will notice." An exchange ledger closes the page: 61 size swaps last year, 54 of them a 30 going back for a 20, so "when in doubt, buy the 20."

One array of two sizes drives the columns, each with a nested spec array, a bestFor line, and an honest line. The ledger below is a single card that settles the question the two columns opened.

When to use

Reach for this block on a two size product line where the choice is the whole decision, after the size and fit guide or in a buying guide. The exchange counts cited must match the real return ledger or the closing line loses its nerve.

A natural flow around it on an Ecommerce Pro page:

Before

• Product overview

After

• Comparison table
• Ask before you buy

What you can display

One strong use is the two size decision with the exchange ledger. Other side by side editions:

• Two model compare. A base and a pro variant with the spec rows that actually differ named plainly.
• Fit picker. Regular against tall, each with the body type it is cut for and the honest tradeoff.
• Capacity ladder. Small against large with the trip length each was built to carry.

Tip: the exchange ledger is what turns a spec table into advice; "the ledger has been saying so for three years straight" is the line that makes the pick for the reader.