Quick answer: There are 7 heavy letters in Arabic: خ ص ض غ ط ق ظ, remembered with the phrase خُصَّ ضَغْطٍ قِظْ (khussa daghtin qiz). They are called Huroof-e-Musta'liyah (letters of rising) because the back of the tongue rises towards the roof of the mouth. They are always read heavy (Tafkheem), with Fatha, Kasra, Damma or sukoon. Three more letters, Ra, the Lam in the name Allah, and Alif, are heavy only in certain cases. All other letters are light (Tarqeeq).
In our one-to-one Tajweed classes, heavy letters are one of the first things we fix, because one thin Saad or a Qaaf that sounds like Kaaf changes the word itself. This guide is the same method our teachers use with children and adults: learn the 7 letters, hear the 5 levels of heaviness, then practise with real Quran words until the difference is automatic.

Four of the seven, ص ض ط ظ, are the heaviest. For these, the tongue does not only rise, it also presses up and covers the sound. This is called Itbaq (closing). The other three, خ غ ق, have rising (Isti'laa) without Itbaq.
| Letter | Name | Where it is made (Makhraj) | Itbaq? | Quran example | Common mistake |
|---|---|---|---|---|---|
| خ | Khaa | Top of the throat (nearest the mouth) | No | خَالِدِينَ (2:162) | Turning it into a "k" or a soft "h" |
| ص | Saad | Tongue tip near the lower front teeth, with a whistle | Yes | الصِّرَاطَ (1:6) | Saying a thin English "s" |
| ض | Daad | Side edge of the tongue against the upper molars | Yes | الضَّالِّينَ (1:7) | Turning it into "d", "z" or ظ |
| غ | Ghain | Top of the throat, with voice | No | غَيْرِ (1:7) | Making it thin like a French "r" |
| ط | Taa | Tongue tip at the roots of the upper front teeth | Yes | الطَّارِقُ (86:2) | Saying an English "t" with a puff of air |
| ق | Qaaf | Deepest part of the tongue against the soft palate | No | قُلْ (112:1) | Saying an English "k" |
| ظ | Zhaa | Tongue tip at the edges of the upper front teeth | Yes | ظُلُمَاتٍ (2:17) | Saying "z" or a thin ذ |

A heavy letter is always heavy, but not always equally heavy. Many teachers explain this with five levels, from fullest to least full:
| Level | The heavy letter has | Quran example |
|---|---|---|
| 1 (fullest) | Fatha with an Alif after it | الصَّاخَّةُ (80:33) خَالِدِينَ (2:162) |
| 2 | Fatha | الصَّمَدُ (112:2) |
| 3 | Damma | غُلِبَتِ (30:2) قُلْ (112:1) |
| 4 | Sukoon | مَقْرَبَةٍ (90:15) أَطْعَمَهُمْ (106:4) الْمُطْمَئِنَّةُ (89:27) |
| 5 (least full) | Kasra | قِيلَ (2:11) الصِّرَاطَ (1:6) |
Some teachers use a simpler three-level scheme (by vowel only), and many give a heavy letter with sukoon the level of the vowel before it. Either way, the key point is the same: even at level 5 the letter stays heavy. قِيلَ must not sound like the English word "keel".

Each pair below is made in nearly the same place. Swapping them is a clear mistake (Lahn-e-Jali) because it changes the word: س / ص, ت / ط, د / ض, ذ / ظ, ك / ق. For example the Kaaf in وَكَلْبُهُمْ (18:18) stays light, while the Qaaf in قُلْ (112:1) is heavy.

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| Day | What to practise (10 minutes) |
|---|---|
| 1 | Learn خُصَّ ضَغْطٍ قِظْ by heart; say each letter with sukoon after a Hamza. |
| 2 | Each letter with Fatha, Kasra, Damma, then with Fatha + Alif (level 1). |
| 3 | The light/heavy pairs: س ص, ت ط, د ض, ذ ظ, ك ق. |
| 4 | Read Surah Al-Fatiha slowly and point out every heavy letter (ص ض غ ط ق). |
| 5 | The 5 levels with the Quran words in the table above. |
| 6 | Lam of Allah and Alif: heavy or light? Mark them in Surah Al-Ikhlas and Surah An-Nas. |
| 7 | Record yourself reciting Juz Amma's short surahs and compare with a teacher or a trusted Qari. |
Children usually learn heavy letters in the Noorani Qaida with Tajweed stage, right after the throat letters. Next steps: Qalqalah letters, Ra rules and Madd letters.
Seven: خ ص ض غ ط ق ظ. Ra, the Lam in the name Allah and Alif are heavy only in certain cases.
خُصَّ ضَغْطٍ قِظْ (khussa daghtin qiz). It is from Imam Ibn al-Jazari's Muqaddimah, the classic Tajweed poem.
Yes. With Kasra they are at the lowest level of heaviness, but they are never read light.
"Bold", "thick", "full-mouth" and "heavy" letters are the same group: the 7 letters of Isti'laa, خ ص ض غ ط ق ظ.
ص ض ط ظ, because they have Itbaq (the tongue presses up and covers the sound) as well as rising.
Tafkheem means making a letter heavy (full mouth); Tarqeeq means making it light (thin sound).
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