Decimal numerals

In standard formal Czech, a noun immediately following a decimal numeral is generally placed in the genitive singular (2. pád jednotného čísla).

Why Genitive Singular?
Decimals are read aloud as fractions. For example, 2,5 litru is read as dvě celé pět desetin litru (two wholes and five tenths of a litre). The implicit word desetin (tenths)—or setin (hundredths), tisícin (thousandths) depending on the number of decimal places—requires the partitive genitive of the single unit being measured. Note that in spoken Czech, native speakers usually drop the word desetin entirely (saying just dvě celé pět litru). While the formal standard keeps the noun in the genitive singular even when desetin is dropped, in everyday speech this omission frequently causes the grammar to shift (as explained in the Everyday Usage section below). Important: Note that Czech uses a decimal comma (desetinná čárka) where English uses a decimal period. When reading left-to-right, the decimal comma itself is the exact trigger for the word celá, celé, or celých. Because the word celá acts as an adjective modifying the hidden feminine noun celá část (whole part) or celá jednotka (whole unit), the integer is read as feminine (e.g., jedna celá, dvě celé, and for 5 and above, the genitive plural pět celých). These feminine forms are the only strictly formal standard, regardless of the counted noun's gender. While native speakers sometimes mistakenly match the integer's gender to the noun in everyday speech (e.g., saying jeden celý pět desetin milionu instead of the correct jedna celá pět desetin milionu), the Czech Language Institute (ÚJČ) considers this an agrammatical link and rejects it for cultivated Czech. Additionally, the formal rule dictates that the decimal digits must also be read as feminine to agree with the hidden desetiny or setiny. For example, 5,1 is formally read as pět celých jedna (not jeden), and 1,2 is jedna celá dvě (not dva). However, when the word desetiny is omitted, reading the fraction part with masculine/neuter digits (e.g., 1,2 as jedna celá dva) is also a standard alternative. For decimals with two or more places (e.g., 3,14), one formal standard is to read the fractional orders (e.g., tři celé čtrnáct setin). However, reading the digits individually (e.g., tři celé jedna čtyři) is also a standard, accepted practice, and is the preferred method in mathematics, technical contexts, and for numbers with many decimal places. When a decimal starts with a zero (e.g., 0,8), it is read as nula celých or žádná celá (zero wholes / no wholes).

Key Rules:

• The rule applies no matter what the integer before the comma is: 0,5 kilometru, 1,5 kilometru, 10,5 kilometru.
• It applies to large scale words too: 1,5 milionu, 2,4 miliardy.
• Compound numerals: When reading compound numerals before the decimal comma (e.g., 25, 34), you must use the non-inverted form. For example, 25,4 is read as dvacet pět celých čtyři, never as pětadvacet celých čtyři.
• Exception for plural-only nouns: Nouns that only exist in the plural (pomnožná jména) must take the genitive plural instead (e.g., 0,5 prázdnin, though using decimals with plural-only nouns is extremely rare).
• This is the strictly prescribed standard for formal writing, news, official documents, and cultivated speech.

Verb Agreement:
When a decimal numeral acts as the subject of a sentence, the primary formal rule is that the verb agrees with the spoken grammatical form of the fraction (e.g., tenths, hundredths). For example, it takes feminine singular for 1 tenth (e.g., zbyla 3,1 litru for jedna desetina), feminine plural for 2-4 tenths (e.g., zbyly 1,4 litru for čtyři desetiny), and neuter singular for 5 or more tenths or hundredths (e.g., zbylo 1,5 litru for pět desetin, or zbylo 3,11 litru for jedenáct setin). Alternatively, default neuter singular agreement (e.g., zbylo 1,4 litru) is widely tolerated and accepted. Furthermore, if the integer part is 5 or higher (e.g., 6,2), the verb can also agree with the integer, which takes neuter singular (e.g., uspělo 6,2 procenta for šest celých...).

Prepositions and Cases:
Crucially, the strictest formal rule states that the noun remains in the genitive singular even if the phrase is governed by a preposition that requires a different case. The decimal number itself declines to match the preposition, while the noun stays in the partitive genitive. For example, po 1,5 kilometru is formally read as po jedné celé pěti desetinách kilometru (where jedné celé pěti desetinách is in the locative, but kilometru remains genitive). However, when the hidden words (celá, desetin) are dropped in speech, the noun often shifts to match the preposition's case (e.g., po jedna celá pět kilometrech in the locative). This is a common colloquialism often found in working or informal texts, rather than a fully standard formal alternative. Important exceptions are 0,5 and 1,5, which are usually read as půl (half) and jeden a půl (one and a half). Note that the word půl is an indeclinable exception that remains frozen. In oblique cases, the noun and other modifiers take the preposition's case, while půl does not change (e.g., s jedním a půl metrem in the instrumental).

Note on Everyday Usage:
In casual speech and everyday professional environments (such as working texts, presentations, or statistical reports), native speakers often deviate from the standard rule in two ways: either by applying the genitive plural to all decimals (saying 1,5 metrů, influenced by Genitive plural after five and higher numerals), or by matching the noun's case to the last digit (saying 1,2 metry, influenced by Two to four with inanimate and neuter nouns). Additionally, in casual spoken Czech, native speakers frequently drop the word celá/celé entirely. For prices and common measurements, it is very common to read the decimal part as a whole number without celá (e.g., 2,50 Kč as dvě padesát, or 3,14 as tři čtrnáct). In highly informal, fast, or technical speech, native speakers often just say the literal word for comma: čárka (e.g., 3,14 read as tři čárka čtrnáct). Otherwise, they might just read the individual digits (e.g., dva pět litru or nula pět litru). However, the Czech Language Institute (ÚJČ) considers these deviations stylistically lower and advises avoiding them in cultivated speech and formal writing.