The forecast exceeds last year's figure of 27,210 new planes by 2025, due to the inclusion of data for the Russian market for the first time.
World airlines would be operating a total of 36,400 passenger and cargo planes by 2026, twice today's figure of 18,200.
The forecast signals Boeing's confidence in a continued boom in plane sales as airlines continue their recovery from a severe downturn caused by the attacks of Sept. 11, 2001.
But it said more efficient use of planes by airlines and potential government curbs on travel due to environmental concerns might subdue traffic growth over the period.
Boeing published its forecast the week before the Paris Air Show, which traditionally heralds a race for high-profile orders with Airbus, a unit of European aerospace group EADS
Boeing said it expects 5 percent annual growth in passenger traffic up to 2026 and 6.1 percent annual growth in cargo traffic. Last year Boeing forecast a slightly lower 4.9 percent annual growth in passenger traffic and the same rate of growth for cargo.
The threat of government environmental curbs on air travel or travellers cutting their air miles voluntarily could subdue growth over the period, Boeing marketing chief Randy Tinseth said at a presentation in London.
Boeing is working on lighter, more efficient aircraft, he said, such as its new 787 Dreamliner, to help cut fuel costs and address environmental concerns.
"This growth will occur in an environmentally responsible and accountable manner that addresses greenhouse gas reduction efforts," said Tinseth at a briefing at Boeing's London headquarters.
ASIA TO LEAD MARKET
The fast-growing Asia-Pacific region would make it the biggest market in terms of the dollar value of new planes, Boeing said, accounting for 36 percent of the total.
North America would make up 26 percent with Europe, including Russia and other members of the Commonwealth of Independent States, on 25 percent. Latin America, the Middle East and Africa is expected to account for 13 percent.
Tinseth said better data from Russia and other CIS members had allowed the region to included for the first time. He said those countries would account for 1,060 new planes over the next 20 years, worth about $70 billion.
The market for single aisle planes -- currently dominated by Boeing's 737 and rival Airbus' A320 family -- would account for most of the new aircraft, Boeing said, with sales of 17,650 such planes expected by 2026.
But larger, wide-bodied planes would represent the greater share by value. Mid-sized twin-aisle planes -- such as Boeing's 787 Dreamliner and Airbus' A350 -- would account for 6,290 of the new planes, Boeing said.
It expects very large aircraft with more than 400 seats, such as Boeing's 747 jumbo and Airbus' even larger A380, to account for 960 new planes.
Boeing said most growth is expected in the market for planes with 90 to 400 seats, consistent with Boeing's bet that more airlines will want to fly small and mid-sized aircraft between a greater range of airports, rather than fly larger planes between major airports.
It forecast a market for 3,700 new regional planes, with fewer than 90 seats, over the next 20 years. Boeing and Airbus do not build planes aimed at that market.