The Acid Test (also known as the Quick Ratio) is a test of liquidity, in other words a company’s ability to pay its debts. It is simply
Current Assets – Stock
If the answer is less than 1, the company cannot currently pay its debts.
The word “current” is important, so that for example land assets would generally be excluded because of the time taken to realise its value. Stock is excluded since its book value may be misleading, particularly if it is last year’s style.
As with all these measures, it is a starting point to understanding your business. You may, for example, want to think about the timing of income and outgoings. The classic for a new business is having to buy for cash, but being paid at 60 or 90 days (or even longer), The fact that your business appears to pass the acid test may mask problems.