Used to describe the degree or extent of something, often in abstract or measurable contexts. Common in both formal and everyday language.
The extent of the damage is still unknown.
The speed of improvement varies depending on the amount of practice.
This area has a high degree of air pollution.
We conducted a survey to measure the degree of satisfaction.
The treatment is changed according to the severity of the symptoms.
This graph indicates the degree of danger.
加減 refers to a degree that can be adjusted or fine-tuned (like seasoning or temperature), whereas 度合い simply states the level or extent of something without implying control over it.
具合 describes the condition or state of something (like health or how a machine is running), while 度合い describes the numerical or abstract degree of something, so the two are easily mixed up despite their similar 合い ending.
Standard spelling with okurigana, common in news and everyday writing.
Shorter variant without the final い, also common and listed in major dictionaries.
Compound of 度 (do, 'degree') and 合い (ai, 'togetherness' or 'matching'), literally 'degree-matching'. The exact historical derivation is uncertain, but the word has been used since at least the Edo period to express extent or degree.