Which two national flags look most alike?

Chad and Romania. They are identical in design and differ only in the shade of blue, Chad’s being the darker. Romania has been asked to change its flag and has refused.

Which national flag is not a rectangle?

Nepal’s, the only one. It is two stacked pennants, and its exact shape is set out as a geometric construction in the constitution.

Why do published flag colours differ between sources?

Because flag laws usually specify a Pantone chip, a CMYK mix or simply a colour name, and converting any of those to sRGB is lossy. That is why two different "US flag blue" values are both in wide circulation.

Flags

126 national flags with what each colour and symbol represents, the official ratio, and the year the current design was adopted. 73 of them name the flags they are routinely mistaken for, recorded from both sides so it does not matter which one you arrive at.

The pairs that look identical

Chad and Romania are the same tricolour in two shades of blue — Chad’s is the darker. Romania has been asked to change it and has declined.
Indonesia and Monaco are both red over white. The only difference is the ratio: Monaco’s flag is squarer.
Ireland and Ivory Coast are mirror images — green at the hoist on Ireland’s, orange at the hoist on Ivory Coast’s.
Norway and Iceland are the same Nordic cross with the red and blue swapped.
The Netherlands and Luxembourg differ only in the blue, which is noticeably lighter on Luxembourg’s.

The genuinely unusual ones

Nepal is the only national flag that is not a rectangle. Its shape is defined by a geometric construction written into the constitution.
Paraguay is the only one with a different emblem on each side.
Switzerland and Vatican City are the only squares.
Libya flew a plain green field from 1977 to 2011 — the only single-colour national flag there has ever been.

By colour

Every flag

The flag of United States Thirteen horizontal stripes alternating red and white, starting and ending with red, and a blue canton in the top hoist corner holding fifty white five-pointed stars in nine offset rows.
The flag of India Three equal horizontal bands of saffron, white and green, with a navy blue 24-spoke wheel centred on the white band.
The flag of United Kingdom A blue field with a white-edged red upright cross and, behind it, a red diagonal cross offset within a broader white diagonal cross.
The flag of Canada A white square in the centre bearing a red eleven-pointed maple leaf, flanked by two red vertical bands each half the width of the square.
The flag of Japan A plain white field with a large crimson disc at the exact centre, three-fifths of the flag's height across.
The flag of France Three equal vertical bands of blue at the hoist, white, and red.
The flag of China A red field with one large yellow five-pointed star in the upper hoist and an arc of four smaller yellow stars to its right.
The flag of Germany Three equal horizontal bands of black, red and gold.
The flag of Russia Three equal horizontal bands of white, blue and red.
The flag of Brazil A green field with a large yellow rhombus, inside which a blue globe carries 27 white stars and a curved white band reading ORDEM E PROGRESSO.
The flag of Italy Three equal vertical bands of green at the hoist, white, and red.
The flag of Mexico Three equal vertical bands of green, white and red, with the national coat of arms — a golden eagle on a cactus, devouring a snake — centred on the white.
The flag of Australia A blue field with the Union Jack in the canton, a large white seven-pointed star beneath it, and the five stars of the Southern Cross in the fly.
The flag of Spain Three horizontal bands of red, yellow and red, the yellow twice the height of each red band, with the coat of arms toward the hoist.
The flag of South Korea A white field with a red-over-blue circular taegeuk at the centre and four black trigrams, one in each corner.
The flag of Ukraine Two equal horizontal bands, blue over yellow.
The flag of Ireland Three equal vertical bands of green at the hoist, white, and orange.
The flag of Nepal Two stacked crimson pennants with blue borders, the upper bearing a white crescent moon and the lower a white twelve-pointed sun. The only national flag that is not a rectangle.
The flag of Switzerland A square red field with a bold equilateral white cross at the centre that does not reach the edges.
The flag of Netherlands Three equal horizontal bands of red, white and blue.
The flag of Indonesia Two equal horizontal bands, red over white.
The flag of Argentina Three equal horizontal bands of light blue, white and light blue, with a golden Sun of May in the centre.
The flag of Israel A white field with two horizontal blue stripes near the top and bottom edges, and a blue Star of David at the centre.
The flag of New Zealand A blue field with the Union Jack in the canton and four red, white-bordered five-pointed stars in the fly forming the Southern Cross.
The flag of Poland Two equal horizontal bands, white over red.
The flag of Türkiye A red field with a white crescent and a white five-pointed star to its right.
The flag of Greece Nine alternating horizontal stripes of blue and white, with a white cross on a blue square in the upper hoist corner.
The flag of South Africa A green horizontal Y laid on its side, outlined in white and gold, separating a red band above and a blue band below, with a black triangle at the hoist inside the Y.
The flag of Norway A red field with a blue Nordic cross outlined in white, offset toward the hoist.
The flag of Philippines A blue band over a red band, with a white equilateral triangle at the hoist bearing a golden sun with eight rays and three gold five-pointed stars, one at each corner.
The flag of Chad Three equal vertical bands of indigo blue at the hoist, gold and red.
The flag of Denmark A red field with a white Nordic cross whose vertical arm is offset toward the hoist.
The flag of Jamaica A gold diagonal cross dividing the flag into four triangles: green at top and bottom, black at hoist and fly.
The flag of Colombia A yellow band filling the top half, with equal blue and red bands below it. No emblem.
The flag of Pakistan A dark green field with a white crescent and five-pointed star at the centre of the fly, and a white vertical band occupying the quarter nearest the hoist.
The flag of Romania Three equal vertical bands of cobalt blue at the hoist, yellow and red.
The flag of Sweden A blue field with a yellow Nordic cross offset toward the hoist.
The flag of Chile A white band over a red band, with a blue square at the hoist covering the full height of the white band only, bearing a single white five-pointed star.
The flag of Cuba Five horizontal stripes, three blue and two white, with a red equilateral triangle at the hoist bearing a white five-pointed star.
The flag of Egypt Three equal horizontal bands of red, white and black, with the golden Eagle of Saladin centred on the white.
The flag of Palestine Three equal horizontal bands of black, white and green, with a red triangle at the hoist.
The flag of Portugal A green band at the hoist covering two-fifths and a red band covering three-fifths, with an armillary sphere and the national shield over the join.
The flag of Saudi Arabia A green field bearing the Islamic declaration of faith in white Thuluth script, with a horizontal white sword beneath it, point toward the hoist.
The flag of Finland A white field with a blue Nordic cross offset toward the hoist.
The flag of Vietnam A red field with a large five-pointed yellow star at the centre.
The flag of Iceland A blue field with a red Nordic cross outlined in white, offset toward the hoist.
The flag of Puerto Rico Five horizontal stripes, three red and two white, with a blue equilateral triangle at the hoist bearing a white five-pointed star.
The flag of Thailand Five horizontal stripes — red, white, a double-height blue, white, red.
The flag of Belgium Three equal vertical bands of black, yellow and red, on a nearly square flag.
The flag of Czechia A white band over a red band, with a blue triangle extending from the hoist to the centre.
The flag of Malaysia Fourteen alternating red and white horizontal stripes with a blue canton bearing a yellow crescent and a fourteen-pointed yellow star.
The flag of Singapore A red band over a white band, with a white crescent and five white five-pointed stars arranged in a circle in the upper hoist.
The flag of United Arab Emirates A vertical red band at the hoist with three equal horizontal bands of green, white and black filling the rest.
The flag of Vatican City A square flag divided vertically, gold at the hoist and white at the fly, with the crossed keys of St Peter and the papal tiara on the white half.
The flag of Venezuela Three equal horizontal bands of yellow, blue and red, with an arc of eight white five-pointed stars on the blue.
The flag of Austria Three equal horizontal bands of red, white and red.
The flag of Bangladesh A dark green field with a red disc set slightly toward the hoist of centre.
The flag of Iran Three equal horizontal bands of green, white and red, with a red emblem centred on the white and a band of stylised Kufic script repeated along the inner edges of the green and red bands.
The flag of Mozambique Green, black and yellow horizontal bands separated by thin white fimbriations, with a red triangle at the hoist bearing a yellow star, on which sit an open book, a hoe and an AK-47 with a bayonet.
The flag of Nigeria Three equal vertical bands of green, white and green.
The flag of Croatia Three equal horizontal bands of red, white and blue, with the chequered Croatian shield and a crown of five smaller shields at the centre.
The flag of Ghana Three equal horizontal bands of red, gold and green, with a black five-pointed star centred on the gold.
The flag of Kenya Three horizontal bands of black, red and green separated by thin white stripes, with a red, black and white Maasai shield and two crossed spears at the centre.
The flag of Libya A black band filling the centre half of the flag, with red above and green below, and a white crescent and five-pointed star at the centre.
The flag of Morocco A red field with a green interlaced five-pointed star outlined at the centre.
The flag of North Korea A wide red band across the centre edged in white, with blue bands above and below, and a red five-pointed star inside a white disc toward the hoist.
The flag of Paraguay Three horizontal bands of red, white and blue, with a different emblem on each side of the white band — the only national flag whose two faces differ.
The flag of Peru Three equal vertical bands of red, white and red.
The flag of Ethiopia Three equal horizontal bands of green, yellow and red, with a blue disc at the centre bearing a yellow pentagram and rays.
The flag of Lebanon Three horizontal bands of red, white and red, the white twice the height of each red band, with a green cedar tree at the centre.
The flag of Monaco Two equal horizontal bands, red over white, on a near-square flag.
The flag of Cyprus A white field with a copper-coloured silhouette of the island above two crossed green olive branches.
The flag of Ecuador A yellow band filling the top half, with equal blue and red bands below, and the national coat of arms centred over all three.
The flag of Haiti Two equal horizontal bands, blue over red, with a white panel at the centre bearing the coat of arms.
The flag of Iraq Three equal horizontal bands of red, white and black, with the phrase ALLĀHU AKBAR in green Kufic script on the white band.
The flag of Ivory Coast Three equal vertical bands of orange at the hoist, white, and green.
The flag of Qatar A maroon field with a white band at the hoist, the two separated by nine white points forming a serrated edge. The longest national flag in proportion.
The flag of Albania A red field with a black double-headed eagle at the centre.
The flag of Cambodia A double-height red band between two blue bands, with a white three-towered depiction of Angkor Wat at the centre.
The flag of Costa Rica Five horizontal stripes — blue, white, a double-height red, white, blue — with the coat of arms in a white oval toward the hoist on the state version.
The flag of Guatemala Three equal vertical bands of sky blue, white and sky blue, with the coat of arms — a quetzal, a scroll, crossed rifles and swords in a laurel wreath — on the white.
The flag of Jordan Three equal horizontal bands of black, white and green, with a red triangle at the hoist bearing a small white seven-pointed star.
The flag of Luxembourg Three equal horizontal bands of red, white and light blue.
The flag of Sri Lanka A dark red field with a gold lion holding a sword and four gold bo leaves at the corners, beside two vertical stripes of green and orange at the hoist, all within a gold border.
The flag of Uruguay Nine alternating horizontal stripes of white and blue, with a white canton bearing a golden Sun of May.
The flag of Bhutan A field divided diagonally from the lower hoist to the upper fly, yellow above and orange below, with a large white dragon holding jewels straddling the divide.
The flag of Bolivia Three equal horizontal bands of red, yellow and green, with the coat of arms on the yellow band on the state version.
The flag of Greenland A white band over a red band, with a large disc offset toward the hoist whose upper half is red and lower half white — the reverse of the field behind it.
The flag of Serbia Three equal horizontal bands of red, blue and white, with a coat of arms — a crowned double-headed eagle — set toward the hoist.
The flag of Bosnia and Herzegovina A blue field with a yellow right triangle along the top edge and a diagonal line of white stars along the triangle's hypotenuse, the top and bottom stars cut off by the flag's edges.
The flag of Honduras Three horizontal bands of turquoise, white and turquoise, with five turquoise five-pointed stars arranged in an X on the white band.
The flag of Malta Two equal vertical bands, white at the hoist and red, with a grey George Cross edged in red in the upper hoist corner.
The flag of Moldova Three equal vertical bands of blue, yellow and red, with the national coat of arms — an eagle holding a cross, with an aurochs head on its shield — on the yellow.
The flag of Mongolia Three equal vertical bands of red, blue and red, with a golden Soyombo emblem on the band nearest the hoist.
The flag of Panama Quartered: white with a blue star at the top hoist, plain red at the top fly, plain blue at the bottom hoist, and white with a red star at the bottom fly.
The flag of Senegal Three equal vertical bands of green, yellow and red, with a green five-pointed star on the yellow.
The flag of Slovakia Three equal horizontal bands of white, blue and red, with a shield bearing a white double cross on three blue hills, set toward the hoist of centre.
The flag of Slovenia Three equal horizontal bands of white, blue and red, with a coat of arms showing Mount Triglav and three gold stars in the upper hoist corner.
The flag of Tunisia A red field with a white disc at the centre containing a red crescent and a red five-pointed star.
The flag of Turkmenistan A green field with a white crescent and five white stars at the upper hoist, and a vertical red stripe near the hoist containing five carpet guls above two crossed olive branches.
The flag of Bahrain A red field with a white band at the hoist, separated by five white triangular points.
The flag of Belize A blue field with narrow red stripes top and bottom, and a large white disc at the centre carrying a coat of arms with two woodcutters, a mahogany tree and a shield of tools.
The flag of Estonia Three equal horizontal bands of blue, black and white.
The flag of Kosovo A blue field with a gold silhouette of the territory below an arc of six white five-pointed stars.
The flag of Kuwait Three equal horizontal bands of green, white and red, with a black trapezoid at the hoist spanning the full height.
The flag of Papua New Guinea A field divided diagonally from the top hoist to the bottom fly: the upper fly half red with a golden bird of paradise, the lower hoist half black with the five white stars of the Southern Cross.
The flag of Cameroon Three equal vertical bands of green, red and yellow, with a yellow five-pointed star centred on the red.
The flag of El Salvador Three horizontal bands of blue, white and blue, with the coat of arms — a triangle enclosing five volcanoes, a liberty cap and a rainbow — on the white.
The flag of Kyrgyzstan A red field with a yellow sun of forty rays at the centre, crossed inside by two sets of three lines forming the frame of a yurt roof.
The flag of Latvia A dark carmine field crossed by a narrow white horizontal band that occupies the middle fifth.
The flag of Liechtenstein Two equal horizontal bands, blue over red, with a gold princely crown in the upper hoist quarter.
The flag of Mali Three equal vertical bands of green, yellow and red, with no emblem.
The flag of South Sudan Black, red and green horizontal bands separated by thin white stripes, with a blue triangle at the hoist bearing a gold five-pointed star.
The flag of Sudan Three equal horizontal bands of red, white and black, with a green triangle at the hoist.
The flag of Andorra Three vertical bands of blue, yellow and red, the yellow slightly wider, with a quartered coat of arms at the centre.
The flag of Dominica A green field with a centred cross of three stripes — yellow, black and white — and a red disc at the centre bearing a purple sisserou parrot ringed by ten green stars.
The flag of Fiji A light blue field with the Union Jack in the canton and the shield from the coat of arms in the fly.
The flag of Guyana A green field with a red triangle at the hoist edged in black, and a longer yellow arrowhead triangle edged in white pointing to the fly.
The flag of Lesotho Three horizontal bands of blue, white and green, the white double height, with a black mokorotlo hat centred on it.
The flag of Maldives A red field with a large green rectangle at the centre bearing a white crescent, its points facing the fly.
The flag of Mauritania A green field with a horizontal gold crescent, points upward, above which sits a gold five-pointed star, and with a red horizontal band at the top and bottom edges.
The flag of Eswatini Blue bands top and bottom with a wide crimson band between them edged in yellow, carrying a black-and-white Nguni shield laid horizontally over two spears and a staff hung with feather tassels.
The flag of Palau A light blue field with a large yellow disc set slightly toward the hoist of centre.
The flag of San Marino Two equal horizontal bands, white over light blue, with the coat of arms — three towers on three peaks, in a wreath, under a crown — at the centre.
The flag of Marshall Islands A dark blue field crossed by two diagonal stripes — orange over white — widening as they rise from the lower hoist to the upper fly, with a large white 24-pointed star in the upper hoist.
The flag of Nauru A blue field with a narrow gold horizontal stripe across the centre and a white twelve-pointed star below it, toward the hoist.

Common questions

Which two national flags look most alike?: Chad and Romania. They are identical in design and differ only in the shade of blue, Chad’s being the darker. Romania has been asked to change its flag and has refused.
Which national flag is not a rectangle?: Nepal’s, the only one. It is two stacked pennants, and its exact shape is set out as a geometric construction in the constitution.
Why do published flag colours differ between sources?: Because flag laws usually specify a Pantone chip, a CMYK mix or simply a colour name, and converting any of those to sRGB is lossy. That is why two different "US flag blue" values are both in wide circulation.