“Is it bigger than a breadbox?”

“Is it bigger than a breadbox?” (or “Is it bigger than a bread box?”) was a catchphrase on the television game show What’s My Line?. Like the game of “Twenty Questions,” the WML celebrity panel tried to find the mystery behind a guest by asking several questions. Comedian Steve Allen asked “Is it bigger than a breadbox?” on the January 18, 1953 show. Allen hadn’t raised the question as a joke, but the audience laughed at it. Allen then repeated the question on subsequent shows.
 
In Steve Allen’s 1960 autobiography, he believed that the breadbox was familiar and a little old-fashioned, adding alliteration to the phrase. The original What’s My Line? ended in 1967 and the “bigger than a breadbox” phrase is about as dated as breadboxes.
 
   
Wikipedia: Breadbox
A breadbox, also called a bread bin, particularly in British English, is a container for storing bread and other baked goods to keep them fresh. They were a common household kitchen item until bread started being made commercially with food preservatives and wrapped in plastic. Breadboxes are still used, especially by people who bake bread at home. Newer ones are usually made of metal. In the past they were often made of wood or sometimes pottery (pottery breadboxes are also called bread crocks). Old breadboxes can be collectible antiques.

The lid or door to a breadbox is usually hinged, opening from the front or top, or a fully removable top. Most breadboxes are fairly tightly sealed when closed, helping to trap moisture and prevent their contents from drying out and going stale. They protect their contents from mice and other pests.
 
As a saying
The most common reference to breadboxes is the phrase “Is it bigger than a breadbox?” when trying to guess what some surprise object may be. This question was popularized by Steve Allen on the American game show What’s My Line? and remains a popular question in the parlor game 20 Questions (despite many young people today not being aware of what a breadbox is). Breadboxes are most commonly big enough to fit one or two average size loaves of bread — about 12 inches wide by 6 inches high and deep (30 cm x 15 cm x 15 cm).
 
Wikipedia: What’s My Line?
What’s My Line? is a weekly panel game show which was produced by Mark Goodson and Bill Todman for CBS television. When first sold to CBS, the proposed title was Occupation Unknown. The original series, which was usually broadcast live, debuted on Thursday, February 2, 1950 at 8:00 p.m. ET and aired on alternating weeks. On Wednesday, April 12, 1950, the broadcast was moved to alternate Wednesday evenings at 9:00 p.m. ET. On Sunday, October 1, 1950, CBS moved the show to weekly on Sundays at 10:30 p.m. ET, where it would remain until the end of its network run.
 
The original series ran for eighteen seasons, ending its run on September 3, 1967. It is the longest-running game show in the history of prime time network television.
 
From 1968 to 1975, a daily (Monday to Friday) revival was produced by Goodson-Todman Productions for syndication, and was distributed by CBS Enterprises, which was renamed Viacom Enterprises in 1971. During its run, What’s My Line? won three Emmy Awards for “Best Quiz or Audience Participation Show,” in 1952, 1953 and 1958.
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The show popularized the phrase, “Is it bigger than a breadbox?” A slight variation of this question was first posed by Steve Allen on January 18, 1953, during his tenure as a regular panelist. Over several subsequent episodes, he refined his breadbox question. Soon, other panelists were asking this question as well, often crediting Allen, and they continued to do so until the end of the series.
 
Wikipedia: Steve Allen
Steve Allen, born Stephen Valentine Patrick William Allen (December 26, 1921(1921-12-26) – October 30, 2000), was an American television personality, musician, actor, comedian, and writer. Though he got his start in radio, Allen is best-known for his television career. He first gained national attention as a guest host on Arthur Godfrey’s Talent Scouts. He graduated to become the first host of The Tonight Show, where he was instrumental in innovating the concept of the television talk show. Thereafter, he hosted numerous game and variety shows, including the Steve Allen Show, I’ve Got a Secret, The New Steve Allen Show, and was a regular panel member on CBS’ What’s My Line?
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He was a regular on the popular panel game show What’s My Line? (where he coined the popular phrase, “Is it bigger than a breadbox?”) from 1953 to 1954 and returned frequently as a panelist after Fred Allen died in March 1956, until the series ended in 1967.
       
YouTube
Steve Allen’s breadbox on What’s My Line?
From 1953, Is it bigger than a breadbox? Is it smaller than a breadbox? No it’s a contestant who makes breadboxes. 
   
3 November 1953, Napa (CA) Register, “Best for What Ails You Is Good Laugh” by Tom E. Danson, pg. 11, cols. 5-6:
BOUND TO HAPPEN…John Daly tried to put over a quickie on Steve Allen on a recent telecast of “What’s My Line,” but the quick-witted Allen was more than ready. Steve had a stock question which he uses on practically every contestant on the popular panel show. The question—“Is it (the product) bigger than a bread box?” Daly tried to cross up Allen by bringing a man who makes bred boxes, but Steve, with the help of audience laughter, caught on quickly and named the man’s occupation first time around.
 
6 March 1957, New Mexican (Santa Fe, NM), pg. 9A, col. 1:
Rigney’s problem is bigger than a bread box.
 
Google News Archive
14 July 1957, St. Petersburg (FL) Times, Sunday magazine, pg. 16, col. 2:
Measuring 374 feet stem to stern, the Admiral is longer than a football field and bigger than a breadbox.
   
Google Books
Mark It and Strike It: an autobiography
By Steve Allen
New York, NY: Holt, Rinehart and Winston
1960
Pg. 203:
One evening, in trying to determine the size of an object that was manufactured by one of the guests, I said, “Is it bigger than a breadbox?” I meant this in all seriousness, but for some reason the audience laughed uproariously. Perhaps the reason is that the breadbox is an old-fashioned item to today’s homemakers and so the word had the sort of connotation that surrounds phrases ...
 
Google News Archive
1 July 1967, The Times (Ottawa), pg. 100 ad:
The exuberant humour of Steve Allen.
BIGGER THAN A BREADBOX.
Illustrated by Rowland B. Wilson with commentary by Leonard Feather
Here is an entertaining selection of the famous Allen humour from his early days in radio, through the Tonight SHow, to his present celebrated night club appearances. “Bigger Than a Breadbox” superbly demonstrates why Steve Allen is not only one of America’s most hilarious humourists, but one of its most respected. $5.95.
   
Google Books
Bigger Than a Breadbox
By Steve Allen, Leonard G. Feather
Published by Doubleday
1967