Numbers in Welsh

In Brief

Modern Welsh builds numbers from 11 to 99 with a regular decimal pattern: tri deg pump is “thirty-five” (literally “three ten five”). Before a noun, however, you must also watch its gender and initial sound: dau gi means “two dogs,” dwy gath means “two cats,” and the noun normally stays singular.

Overview

Welsh cardinal numbers—the numbers used for counting and saying how many—are an A1 essential. You need them for prices, phone numbers, ages, addresses, travel, and quantities. The basic forms are easy to learn, and the modern decimal system closely resembles English in the way it groups numbers into tens and units.

The main difference from English appears when a number stands before a noun (a word for a person, place, thing, or idea). Welsh distinguishes masculine and feminine forms of two, three, and four. Some numbers also trigger an initial mutation: the first consonant of the following word changes in a predictable way. In addition, a counted noun is normally singular: Welsh says dau gi, literally “two dog,” where English requires “two dogs.”

Start by learning 1–10 and the decimal tens. Then add three practical rules: choose the gendered form, use a singular noun, and apply any required mutation. The later section on the traditional counting system is useful for recognition, but beginners do not need to master it immediately.

How It Works

The numbers 0–10

Number	Welsh	Before a noun / note
0	sero	Usually sero
1	un	Soft-mutates a feminine noun where possible
2	dau / dwy	dau with masculine nouns; dwy with feminine nouns; soft mutation
3	tri / tair	tri with masculine nouns and aspirate mutation; tair with feminine nouns and no mutation
4	pedwar / pedair	pedwar masculine; pedair feminine; no mutation
5	pump	Usually pum immediately before a noun
6	chwech	Usually chwe immediately before a noun; aspirate mutation
7	saith	No special form before a noun
8	wyth	No special form before a noun
9	naw	No special form before a noun
10	deg	No gender distinction

The slash in dau/dwy, tri/tair, and pedwar/pedair does not mean that the forms are freely interchangeable. The choice depends on the grammatical gender of the noun. For example, ci “dog” is masculine, while cath “cat” is feminine:

• dau gi — two dogs
• dwy gath — two cats
• tri chi — three dogs
• tair cath — three cats
• pedwar ci — four dogs
• pedair cath — four cats

Building 11–99 with the modern decimal system

In the decimal system, deg means “ten.” Put the number of tens before deg, then add the units:

Number	Welsh	Pattern
10	deg	ten
11	un deg un	one ten one
12	un deg dau	one ten two
20	dau ddeg	two tens; deg is soft-mutated after dau
21	dau ddeg un	two tens one
30	tri deg	three tens
35	tri deg pump	three tens five
40	pedwar deg	four tens
50	pum deg	five tens
60	chwe deg	six tens
70	saith deg	seven tens
80	wyth deg	eight tens
90	naw deg	nine tens
99	naw deg naw	nine tens nine
100	cant	one hundred

Notice three changes inside the tens themselves:

1. dau + deg becomes dau ddeg, because dau causes soft mutation.
2. pump shortens to pum before deg.
3. chwech shortens to chwe before deg.

When a compound number ends in two, three, or four and directly counts a noun, the final unit can show that noun’s gender: pedwar deg dwy bunt “forty-two pounds,” because punt is feminine. In everyday speech, particularly with larger quantities, an o + plural noun construction is also very useful: tri deg pump o fyfyrwyr “thirty-five students.” The preposition o means “of” and causes its own soft mutation, which explains forms such as o bobl from pobl, “people.”

Use a singular noun after a number

After an exact number, Welsh normally uses the singular form of a countable noun:

Welsh	Literal structure	Natural English
dau lyfr	two book	two books
tair awr	three hour	three hours
pum munud	five minute	five minutes
deg punt	ten pound	ten pounds

This is one of the strongest contrasts with English. Do not build the Welsh phrase by taking an English plural and placing a number before it. Learn the number and the singular noun as one unit.

For larger or heavier phrases, Welsh often uses number + o + plural instead: cant o bobl “a hundred people.” Both patterns are part of normal Welsh; the direct singular pattern is especially important with small numbers, measurements, time, and money.

Mutations after numbers

A mutation changes the beginning of a word without changing its basic meaning. Two mutation types matter here:

• Soft mutation changes several initials, including c → g, p → b, t → d, b → f, d → dd, g → zero, m → f, and ll → l.
• Aspirate mutation affects only c → ch, p → ph, and t → th.

The practical number rules are:

Number	Rule	Example
un	Soft mutation of a feminine noun	un gath “one cat” (cath → gath)
dau	Masculine noun + soft mutation	dau frawd “two brothers” (brawd → frawd)
dwy	Feminine noun + soft mutation	dwy gath “two cats” (cath → gath)
tri	Masculine noun + aspirate mutation	tri chi “three dogs” (ci → chi)
tair	Feminine noun; no mutation caused by the number	tair cath “three cats”
chwe	Aspirate mutation	chwe phunt “six pounds” (punt → phunt)

A mutation is visible only if the word begins with an affected consonant. That is why dwy chwaer “two sisters” keeps ch-: soft mutation has no form for ch. Likewise, the aspirate mutation after tri or chwe makes no visible change to words beginning with b, d, g, m, a vowel, or several other consonants.

The rule after un depends on gender. Compare masculine un ci “one dog,” with no mutation, and feminine un gath “one cat,” with cath → gath. Since English nouns do not have grammatical gender in this way, it helps to learn a Welsh noun together with its gender rather than trying to guess later.

Standalone forms and forms before nouns

Use pump and chwech when simply counting or when the number stands alone:

• pedwar, pump, chwech — four, five, six
• Faint? Pump. — How many? Five.

Before a following noun or deg, the usual forms are pum and chwe:

• pum llyfr — five books
• chwe mis — six months
• pum deg — fifty
• chwe deg — sixty

Examples in Context

Welsh	English	Note
Mae un ci ac un gath yn yr ardd.	There is one dog and one cat in the garden.	Feminine cath soft-mutates after un.
Mae dau frawd yn aros tu allan.	Two brothers are waiting outside.	Masculine brawd becomes frawd after dau.
Mae dwy chwaer yn byw yma.	Two sisters live here.	dwy agrees with feminine chwaer; ch- has no soft-mutated form.
Mae tri chi yn y parc.	There are three dogs in the park.	tri causes ci → chi.
Mae tair cath yn cysgu.	Three cats are sleeping.	tair is the feminine form and does not mutate cath.
Mae pedwar bws yn gadael heddiw.	Four buses are leaving today.	Masculine bws takes pedwar; the noun remains singular.
Arhoson ni am bum munud.	We waited for five minutes.	Use pum, not standalone pump, before munud.
Mae chwe phunt ar y bwrdd.	There are six pounds on the table.	chwe causes aspirate mutation: punt → phunt.
Mae'r ystafell yn costio saith deg punt.	The room costs seventy pounds.	A round decimal number followed by singular punt.
Rhif y bws yw wyth deg naw.	The bus number is eighty-nine.	The number stands alone, so no noun agreement is needed.
Mae'r tocyn yn costio pedwar deg dwy bunt.	The ticket costs forty-two pounds.	Final dwy agrees with feminine punt, which soft-mutates to bunt.
Mae tri deg pump o fyfyrwyr yn y dosbarth.	There are thirty-five students in the class.	A larger number with o + plural.
Mae cant o bobl yma.	There are a hundred people here.	o causes pobl → bobl.

Common Mistakes

Using a plural noun after the number

• Wrong: dau lyfrau
• Right: dau lyfr
• Why: A noun counted directly after a Welsh number is normally singular. Llyfrau is the plural “books”; llyfr is the singular “book.”

Ignoring the noun’s gender

• Wrong: dau cath
• Right: dwy gath
• Why: cath is feminine, so “two” must be dwy. It also triggers soft mutation, changing cath to gath.

Treating tri and tair as interchangeable

• Wrong: tri cath
• Right: tair cath
• Why: Use masculine tri but feminine tair. Only tri triggers aspirate mutation; tair does not.

Forgetting the aspirate mutation

• Wrong: tri ci; chwe punt
• Right: tri chi; chwe phunt
• Why: tri before a masculine noun and chwe cause aspirate mutation when the next word begins with c, p, or t.

Using standalone pump and chwech before a noun

• Wrong: pump munud; chwech mis
• Right: pum munud; chwe mis
• Why: pump and chwech are the usual standalone forms; before another word, use pum and chwe.

Copying English tens in reverse order

• Wrong: pump tri deg for 35
• Right: tri deg pump
• Why: In the modern decimal system, say the tens first, then the units: “three tens five.”

Usage Notes

Welsh has both the modern decimal system taught here and an older vigesimal system based partly on twenties. The decimal forms are clear, productive, and widely used in education and many everyday contexts. Nevertheless, traditional forms remain common enough that learners will encounter them, especially in ages, dates, time, set expressions, and the speech of some speakers.

For telephone numbers, codes, and reference numbers, speakers may read digits individually rather than treating the whole sequence as one quantity. In that setting, use the standalone counting forms, including pump and chwech. Prices and measurements, by contrast, normally form a number phrase with a noun: pum punt, chwe milltir, deg munud.

Mutations can overlap with other grammar in a complete sentence. For example, the form of the number itself may mutate because of a preceding word, even while that number causes a mutation in the noun after it. This is why learners may hear ddwy rather than dictionary-form dwy in some sentences. Identify the core phrase first—such as dwy chwaer—then account for the wider sentence separately.

Beyond the Basics

You do not need to produce the traditional system at A1, but you should gradually learn to recognise frequent forms. Un ar ddeg is eleven, deuddeg is twelve, ugain is twenty, deugain is forty, trigain is sixty, and pedwar ugain is eighty. Thus the same quantity may have a decimal and a traditional expression depending on context and speaker.

Value	Modern decimal	Traditional form commonly encountered
11	un deg un	un ar ddeg
12	un deg dau	deuddeg
20	dau ddeg	ugain
40	pedwar deg	deugain
60	chwe deg	trigain
80	wyth deg	pedwar ugain

Traditional compounds have their own patterns, mutations, and gender-sensitive forms. Learn them as complete expressions rather than trying to convert every decimal number word by word. In particular, clock time often preserves traditional number forms, so the related topic of time and dates deserves separate study.

At higher levels, you will also meet ordinal numbers (numbers indicating order, such as “first” and “second”) and fractions. These are not formed by merely placing the cardinal number before a noun: Welsh uses forms such as cyntaf “first,” ail “second,” hanner “half,” and chwarter “quarter.”

Practice Tips

1. Build in layers. First recite 1–10, then make the tens from 20 to 90, and finally add random units: chwe deg, chwe deg saith, chwe deg naw.
2. Learn gender and mutation together. Make paired cards such as dau gi / dwy gath, tri chi / tair cath, and pedwar ci / pedair cath. Saying both sides makes the contrast easier to remember.
3. Count real things aloud. Use objects, prices, and short waits around you: pum munud, chwe phunt, saith llyfr. Check that the noun is singular and that you have used pum/chwe before it.

Related Concepts

• Next step: Time and Dates — apply numbers to clock times, dates, months, and everyday scheduling.
• Later extension: Ordinal Numbers and Fractions — learn forms for order and parts, including “first,” “second,” “half,” and “quarter.”