If we think that at least one million people are required be a real city, then there are 428 cities in the world.

Of course this is highly subjective. Countries and regions have different ideas of defining city limits. Demographers instead like to talk about agglomerations, where several adjoining towns have a high degree of inter-dependence that they virtually form a single identity, such as in the case of the Ruhr or Chongquing. The same can happen when a few large cities are close together(e.g.: Dallas and Fort Worth, Basel, Freiburg and Mulhouse), or if a smaller city becomes part of a sprawling larger city (e.g.: Yokohama, Leeds, San Jose). Cross-national comparisions are always dodgy due to different timescales and data definitions, especially when in developing countries there is a large segment of the population that is undocumented or migratory.

Naturally countries with a large number of people will have more cities. Urbanisation is likely to be high in the developed world, as well as in physically large countries with expanses of inhospitable terrain, like Saudi Arabia, Brazil and Australia. Conversely, European countries are more likely to have population density centred on their capitals. Only eight countries have ten or more cities with one million or more inhabitants:

USA:	   54 cities
China:      48 cities
India:      42 cities
Brazil:     20 cities
Russia:     15 cities
Japan:      14 cities
Germany:    11 cities
Mexico:     10 cities

Conversely, France, Spain and Italy each have only four such cities.

Below are the 428 cities in the world with an estimated population of one million people or greater. Where possible the details of any other cities that are counted are included.

34,000,000: Tokyo (Tōkyō), Japan (also includes: Yokohama, Kawasaki)
22,350,000: Mexico City (Ciudad de México), Mexico (also includes: Nezahualcóyotl, Ecatepec, Naucalpan)
22,050,000: Seoul (Sŏul), South Korea (also includes: Bucheon, Goyang, Incheon, Seongnam, Suweon)
21,800,000: New York, USA (also includes: Newark, Paterson)
20,000,000: Sao Paulo (São Paulo), Brazil (also includes: Guarulhos)
19,400,000: Bombay (Mumbai), India (also includes: Kalyan, Thane, Ulhasnagar)
19,000,000: Delhi, India (also includes: Faridabad, Ghaziabad)
17,750,000: Los Angeles, USA (also includes: Riverside, Anaheim)
16,850,000: Jakarta, Indonesia (also includes: Bekasi, Bogor, Depok, Tangerang)
16,750,000: Osaka (Ōsaka), Japan (also includes: Kobe, Kyoto)
15,350,000: Calcutta (Kolkata), India (also includes: Haora)
15,250,000: Cairo (Al-Qāhirah), Egypt (also includes: Al-Jizah, Shubra al-Khaymah)
14,550,000: Manila, Philippines (also includes: Kalookan, Quezon City)
13,800,000: Karachi (Karāchi), Pakistan
13,650,000: Moscow (Moskva), Russia
13,400,000: Shanghai, China
13,350,000: Buenos Aires, Argentina (also includes: San Justo, La Plata)
12,750,000: Dacca (Dhaka), Bangladesh
12,000,000: Rio de Janeiro, Brazil (also includes: Nova Iguaçu, São Gonçalo)
11,950,000: London, Great Britain
11,650,000: Tehran (Tehrān), Iran (also includes: Karaj)
11,250,000: Istanbul (İstanbul), Turkey
10,800,000: Lagos, Nigeria
10,700,000: Beijing, China
9,900,000: Paris, France
9,700,000: Chicago, USA
8,350,000: Lima, Peru
8,150,000: Bogota (Santa Fe de Bogotá), Colombia
8,050,000: Washington, USA (also includes: Baltimore)
8,000,000: Nagoya, Japan
7,800,000: Chungking (Chongqing), China
7,800,000: Bangkok (Krung Thep), Thailand
7,450,000: Madras (Chennai), India
7,300,000: Hong Kong (Xianggang), China
7,300,000: Lahore, Pakistan
7,200,000: San Francisco, USA (also includes: Oakland, San Jose)
7,150,000: Johannesburg, South Africa (also includes: Soweto, East Rand, West Rand)
6,900,000: Bangalore, India
6,900,000: Taipei (T'aipei), Taiwan
6,800,000: Kinshasa, DR Congo
6,550,000: Hyderabad (Hyderābād), India
6,000,000: Philadelphia, USA
5,950,000: Tientsin (Tianjin), China
5,850,000: Dallas, USA (also includes: Fort Worth)
5,800,000: Ruhr, Germany
5,750,000: Detroit, USA (also includes: Windsor (Canada))
5,700,000: Boston, USA
5,500,000: Khartoum (Al-Khartūm), Sudan
5,450,000: Ahmadabad (Ahmadābād), India
5,450,000: Baghdad (Baghdād), Iraq
5,450,000: Miami, USA (also includes: Fort Lauderdale, West Palm Beach)
5,400,000: Belo Horizonte, Brazil
5,400,000: Riyadh (Ar-Riyād), Saudi Arabia
5,300,000: Santiago, Chile
5,300,000: Houston, USA
5,250,000: Madrid, Spain
5,200,000: St. Petersburg (Sankt-Peterburg, Leningrad), Russia
5,150,000: Toronto, Canada
5,000,000: Atlanta, USA
4,950,000: Canton (Guangzhou), China
4,900,000: Wuhan, China
4,900,000: Alexandria (Al-Iskandarīyah), Egypt
4,900,000: Rangoon (Yangon), Myanmar
4,850,000: Ho Chi Minh City (Thanh Pho Ho Chi Minh, Saigon), Vietnam
4,650,000: Caracas, Venezuela
4,600,000: Harbin, China
4,550,000: Singapore, Singapore
4,500,000: Shenyang, China
4,350,000: Poona (Pune), India (also includes: Pimpri-Chinchwad)
4,300,000: Sydney, Australia
4,250,000: Guadalajara, Mexico (also includes: Zapopan)
4,200,000: Berlin, Germany
4,150,000: Chittagong, Bangladesh
4,150,000: Kuala Lumpur, Malaysia
4,100,000: Algiers (El Djazaïr), Algeria
4,000,000: Porto Alegre, Brazil
4,000,000: Abidjan, Côte d'Ivoire
3,850,000: Chengtu (Chengdu), China
3,850,000: Monterrey, Mexico
3,800,000: Milan (Milano), Italy
3,800,000: Jidda (Jiddah), Saudi Arabia
3,800,000: Barcelona, Spain
3,800,000: Phoenix, USA
3,750,000: Recife, Brazil
3,750,000: Casablanca (Casablanca (Dar-el-Beida)), Morocco
3,750,000: Busan (Busan (Pusan)), South Korea
3,700,000: Ankara, Turkey
3,700,000: Seattle, USA
3,600,000: Melbourne, Australia
3,600,000: Montreal (Montréal), Canada
3,550,000: Surat (Sūrat), India
3,550,000: Pyongyang (P'yŏngyang), North Korea
3,500,000: Athens (Athínai), Greece
3,450,000: Brasília, Brazil
3,450,000: Salvador, Brazil
3,450,000: Durban, South Africa
3,400,000: Medellin (Medellín), Colombia
3,350,000: Fortaleza, Brazil
3,350,000: Rome (Roma), Italy
3,350,000: Minneapolis, USA
3,300,000: Nanking (Nanjing), China
3,300,000: Bandung, Indonesia
3,300,000: Kano, Nigeria
3,250,000: Cape Town (Kaapstad), South Africa
3,250,000: Kiev (Kyyiv), Ukraine
3,200,000: Kabul (Kabol), Afghanistan
3,150,000: Curitiba, Brazil
3,150,000: Kānpur, India
3,150,000: Surabaya, Indonesia
3,150,000: Amman ('Ammān), Jordan
3,050,000: Sian (Xi'an), China
3,050,000: Tel Aviv-Jaffa (Tel Aviv-Yafo), Israel
3,050,000: Naples (Napoli), Italy
3,000,000: Dairen (Dalian), China
3,000,000: Addis Abeba (Adis Abeba), Ethiopia
3,000,000: San Diego, USA
2,950,000: Lisbon (Lisboa), Portugal
2,900,000: Tsingtao (Qingdao), China
2,900,000: Santo Domingo (Santo Domingo (de Guzman)), Dominican Republic
2,900,000: Nairobi, Kenya
2,900,000: Ibadan, Nigeria
2,900,000: Kaohsiung, Taiwan
2,900,000: Dar es Salaam, Tanzania
2,850,000: Jaipur, India
2,850,000: Faisalabad (Lyallpur), Pakistan
2,850,000: Katowice, Poland (also includes the Upper Silesian Area)
2,850,000: Cleveland, USA
2,800,000: Luanda, Angola
2,800,000: San Juan, Puerto Rico
2,800,000: Daegu (Taegu), South Korea
2,800,000: St. Louis, USA
2,750,000: Damascus (Dimashq), Syria
2,750,000: Izmir (İzmir), Turkey
2,700,000: Lucknow, India
2,700,000: Rawalpindi (Rāwalpindi), Pakistan (also includes: Islamabad)
2,700,000: Aleppo (Halab), Syria
2,650,000: Campinas, Brazil
2,650,000: Cali, Colombia
2,650,000: Stuttgart, Germany
2,650,000: Tampa, USA
2,650,000: Denver, USA
2,600,000: Hangchou (Hangzhou), China
2,600,000: Birmingham, Great Britain
2,550,000: Hamburg, Germany
2,550,000: Accra, Ghana
2,550,000: Meshed (Mashhad), Iran
2,550,000: Colombo, Sri Lanka
2,500,000: Zhengzhou, China
2,500,000: Manchester, Great Britain
2,500,000: Sapporo, Japan
2,500,000: Puebla, Mexico
2,450,000: Nagpur (Nāgpur), India
2,450,000: Pittsburgh, USA
2,400,000: Changchun, China
2,400,000: Jinan, China
2,400,000: Shijiazhuang, China
2,400,000: Budapest, Hungary
2,400,000: Warsaw (Warszawa), Poland
2,400,000: Tashkent (Toshkent, Taškent), Uzbekistan
2,350,000: Taichung (T'aichung), Taiwan
2,300,000: Havana (La Habana), Cuba
2,300,000: Medan, Indonesia
2,300,000: Dakar, Senegal
2,300,000: Pretoria, South Africa
2,250,000: Guayaquil, Ecuador
2,250,000: San Salvador, El Salvador
2,250,000: Fukuoka, Japan
2,250,000: Beirut (Bayrūt), Lebanon
2,200,000: Vancouver, Canada
2,200,000: Port-au-Prince, Haiti
2,200,000: Tunis (Tūnis), Tunisia
2,150,000: Taiyuan, China
2,150,000: Leeds, Great Britain
2,150,000: Amsterdam, Netherlands
2,150,000: Maracaibo, Venezuela
2,100,000: Baku (Bakı), Azerbaijan
2,100,000: Kunming, China
2,100,000: Patna, India
2,100,000: Bucharest (Bucureşti), Romania
2,100,000: Sacramento, USA
2,100,000: Portland, USA
2,100,000: Cincinnati, USA
2,100,000: Harare (Harare (Salisbury)), Zimbabwe
2,050,000: Belem (Belém), Brazil
2,050,000: Changsha, China
2,000,000: Indore, India
2,000,000: Chungli, Taiwan
1,975,000: Guatemala City (Ciudad de Guatemala), Guatemala
1,950,000: Munich (München), Germany
1,950,000: Kansas City, USA
1,925,000: Nanchang, China
1,925,000: Frankfurt, Germany
1,900,000: Goiania (Goiânia), Brazil
1,900,000: Donetsk (Donets'k), Ukraine
1,900,000: San Antonio, USA
1,900,000: Orlando, USA
1,875,000: Vienna (Wien), Austria
1,875,000: Brussels (Bruxelles (Brussel)), Belgium
1,875,000: Barranquilla, Colombia
1,850,000: Fuzhou, China
1,850,000: Cologne (Köln), Germany
1,850,000: Isfahan (Esfahān), Iran
1,850,000: Asuncion (Asunción), Paraguay
1,850,000: Montevideo, Uruguay
1,850,000: Indianapolis, USA
1,825,000: Kharkov (Kharkiv), Ukraine
1,800,000: Douala, Cameroon
1,800,000: Valencia, Venezuela
1,775,000: Brisbane, Australia
1,775,000: Minsk, Belarus
1,775,000: Dammam (Ad-Dammām), Saudi Arabia
1,750,000: Zibo, China
1,750,000: Vadodara (Vadodara (Baroda)), India
1,750,000: Maputo, Mozambique
1,750,000: Gujranwala (Gujrānwāla), Pakistan
1,750,000: Nižnij Novgorod (Nižnij Novgorod, Gor'kij), Russia
1,750,000: Hanoi (Ha Noi), Vietnam
1,725,000: La Paz, Bolivia
1,725,000: Lanzhou, China
1,725,000: Bhopal (Bhopāl), India
1,725,000: Hiroshima, Japan
1,725,000: Rabat, Morocco
1,725,000: Stockholm, Sweden
1,725,000: Milwaukee, USA
1,725,000: Columbus, USA
1,700,000: Guiyang, China
1,700,000: Ningbo, China
1,700,000: Palembang, Indonesia
1,700,000: Hyderabad (Hyderābād), Pakistan
1,700,000: Las Vegas, USA
1,675,000: Coimbatore, India
1,675,000: Virginia Beach, USA
1,650,000: Santos, Brazil
1,650,000: Manaus, Brazil
1,650,000: Wuxi, China
1,650,000: Ludhiana (Ludhiāna), India
1,650,000: Antananarivo (Tananarive), Madagascar
1,650,000: Providence, USA
1,625,000: Vitoria (Vitória), Brazil
1,625,000: Kuwait City (Al-Kuwayt), Kuwait
1,625,000: Tijuana, Mexico
1,625,000: Multan (Multān), Pakistan
1,625,000: Cebu, Philippines
1,600,000: Hofei (Hefei), China
1,600,000: Mannheim, Germany
1,600,000: Semarang, Indonesia
1,600,000: Kitakyushu (Kitakyūshū), Japan
1,600,000: Bamako, Mali
1,600,000: Lusaka, Zambia
1,575,000: Anshan, China
1,575,000: Jilin, China
1,575,000: Quito, Ecuador
1,575,000: Agra (Āgra), India
1,575,000: Sendai, Japan
1,575,000: Novosibirsk, Russia
1,550,000: Glasgow, Great Britain
1,550,000: Ciudad Juarez (Ciudad Juárez), Mexico
1,550,000: Mecca (Makkah), Saudi Arabia
1,550,000: Buffalo, USA (also includes St. Catharines (Canada))
1,525,000: Cordoba (Córdoba), Argentina
1,525,000: Khulna, Bangladesh
1,525,000: Conakry, Guinea
1,525,000: Vishakhpatnam (Visākhpatnam, Vishākhpatnam)), India
1,525,000: Kochi (Cochin), India
1,525,000: Yekaterinburg (Jekaterinburg, Sverdlovsk), Russia
1,525,000: Belgrade (Beograd), Serbia and Montenegro
1,525,000: Salt Lake City, USA
1,500,000: Shenzhen, China
1,500,000: Tangshan, China
1,500,000: Turin (Torino), Italy
1,500,000: Kaduna, Nigeria
1,500,000: Charlotte, USA
1,475,000: Yaounde (Yaoundé), Cameroon
1,475,000: Tripoli (Tarābulus), Libya
1,475,000: Taejon (Daejeon (Taejŏn)), South Korea
1,450,000: Perth, Australia
1,450,000: Santa Cruz, Bolivia
1,450,000: Urumqi (Wulumuqi), China
1,450,000: Fushun, China
1,450,000: Marseille, France
1,450,000: Nasik (Nāshik), India
1,450,000: Leon (León), Mexico
1,450,000: Gwangju (Kwangju), South Korea
1,450,000: Bursa, Turkey
1,450,000: Austin, USA
1,425,000: Lyon, France
1,425,000: Tabriz (Tabrīz), Iran
1,425,000: Gaza (Ghazzah), Palestinian Territories
1,425,000: Valencia (València), Spain
1,425,000: Nashville, USA
1,400,000: Copenhagen (København), Denmark
1,400,000: Meerut, India
1,400,000: Toluca, Mexico
1,400,000: Samara (Samara (Kujbyšev)), Russia
1,400,000: Kampala, Uganda
1,400,000: Dnepropetrovsk (Dnipropetrovs'k), Ukraine
1,400,000: Raleigh, USA
1,375,000: Lille, France (also includes: Kortrijk (Belgium))
1,375,000: Benares (Vārānasi), India
1,375,000: Okayama, Japan
1,375,000: Peshawar (Peshāwar), Pakistan
1,375,000: Davao, Philippines
1,375,000: Volgograd, Russia
1,375,000: Mogadishu (Muqdisho), Somalia
1,350,000: Liverpool, Great Britain
1,350,000: Ujungpandang, Indonesia
1,350,000: Porto, Portugal
1,325,000: Phnom Penh (Phnum Pénh), Cambodia
1,325,000: Suzhou, China
1,325,000: San Jose (San José), Costa Rica
1,325,000: Dusseldorf (Düsseldorf), Germany
1,325,000: Madurai, India
1,325,000: Asansol, India
1,325,000: Rostov-na-Donu, Russia
1,325,000: Chelyabinsk (Čel'abinsk), Russia
1,325,000: Tainan (T'ainan), Taiwan
1,325,000: Dubai (Dubayy), United Arab Emirates
1,325,000: New Orleans, USA
1,325,000: Louisville, USA
1,325,000: Sanaa (San'ā'), Yemen
1,300,000: Baotou, China
1,300,000: Xuzhou, China
1,300,000: Jamshedpur, India
1,300,000: Jabalpur, India
1,300,000: Adana, Turkey
1,275,000: Rosario, Argentina
1,275,000: Nanning, China
1,275,000: Prague (Praha), Czech Republic
1,275,000: Sheffield, Great Britain
1,275,000: Memphis, USA
1,275,000: Maracay, Venezuela
1,250,000: Lubumbashi, DR Congo
1,250,000: Mbuji-Mayi, DR Congo
1,250,000: Rajkot (Rājkot), India
1,250,000: Dhanbad (Dhanbād), India
1,250,000: Tanjungkarang (Tanjungkarang, Bandar Lampung), Indonesia
1,250,000: Shiraz (Shīrāz), Iran
1,250,000: Mosul (Al-Mawsil), Iraq
1,250,000: Kathmandu (Kāthmāndau), Nepal
1,250,000: Auckland, New Zealand
1,250,000: Sevilla, Spain
1,250,000: Jacksonville, USA
1,225,000: Yerevan, Armenia
1,225,000: Sao Luis (São Luís), Brazil
1,225,000: Handan, China
1,225,000: Luoyang, China
1,225,000: Brazzaville, Congo
1,225,000: Amritsar, India
1,225,000: Managua, Nicaragua
1,225,000: Panama City (Ciudad de Panamá), Panama
1,225,000: Grand Rapids, USA
1,200,000: Oran (Wahran), Algeria
1,200,000: Natal, Brazil
1,200,000: Sofia (Sofija), Bulgaria
1,200,000: Tbilisi, Georgia
1,200,000: Allahabad (Allahābād), India
1,200,000: Alma-Ata (Almaty), Kazakhstan
1,200,000: Rotterdam, Netherlands
1,200,000: Benin City, Nigeria
1,200,000: Hartford, USA
1,175,000: Qiqihar, China
1,175,000: Richmond, USA
1,175,000: Oklahoma City, USA
1,150,000: Ottawa, Canada
1,150,000: Vijayawada (Vijayawāda), India
1,150,000: Omsk, Russia
1,150,000: Barquisimeto, Venezuela
1,125,000: Adelaide, Australia
1,125,000: Antwerp (Antwerpen, Anvers), Belgium
1,125,000: Maceio (Maceió), Brazil
1,125,000: Shantou, China
1,125,000: Srinagar (Srīnagar), India
1,125,000: Chandigarh (Chandīgarh), India
1,125,000: Naha, Japan
1,125,000: Himeji, Japan
1,125,000: Saratov, Russia
1,125,000: Kazan (Kazan'), Russia
1,125,000: Zurich (Zürich), Switzerland
1,125,000: Greensboro, USA
1,100,000: Ouagadougou, Burkina Faso
1,100,000: Calgary, Canada
1,100,000: Datong, China
1,100,000: Helsinki (Helsinki (Helsingfors)), Finland
1,100,000: Aurangabad (Shambajinagar, Aurangābād), India
1,100,000: Bhilai (Bhilai Nagar), India
1,100,000: Kumamoto, Japan
1,100,000: Hamamatsu, Japan
1,100,000: Torreon (Torreón), Mexico
1,100,000: Lodz (Łódź), Poland
1,100,000: Ufa, Russia
1,100,000: Freetown, Sierra Leone
1,100,000: Port Elizabeth, South Africa
1,100,000: Ulsan, South Korea
1,100,000: Odessa (Odesa), Ukraine
1,100,000: Birmingham, USA
1,075,000: Newcastle upon Tyne, Great Britain
1,075,000: Port Harcourt, Nigeria
1,075,000: Nampo (Namp'o), North Korea
1,075,000: Perm (Perm'), Russia
1,075,000: Medina (Al-Madīnah), Saudi Arabia
1,050,000: Joinville, Brazil
1,050,000: Huhehot (Hohhot (), China
1,050,000: Benxi, China
1,050,000: Bucaramanga, Colombia
1,050,000: Cartagena, Colombia
1,050,000: Nurnberg (Nürnberg), Germany
1,050,000: Ranchi (Rānchi), India
1,050,000: Sholapur (Solāpur (Sholāpur)), India
1,050,000: Dublin (Dublin (Baile Átha Cliath)), Ireland
1,050,000: Gaziantep, Turkey
1,050,000: Rochester, USA
1,050,000: Greenville, USA
1,025,000: Edmonton, Canada
1,025,000: Hanover (Hannover), Germany
1,025,000: Johor Baharu, Malaysia
1,025,000: Fes (Fès), Morocco
1,025,000: Fresno, USA
1,000,000: Joao Pessoa (João Pessoa), Brazil
1,000,000: Huainan, China
1,000,000: Jodhpur, India
1,000,000: Gwalior, India
1,000,000: Basra (Al-Basrah), Iraq
1,000,000: Shizuoka, Japan
1,000,000: San Luis Potosi (San Luis Potosí), Mexico
1,000,000: Krasnojarsk, Russia
1,000,000: Dayton, USA
1,000,000: Albany, USA
1,000,000: Haiphong (Hai Phong), Vietnam

ref: www.citypopulation.de