There is no single formula which is accepted and used in the process of valuing businesses. Obviously, a business seller will seek to drive the price up, whereas any possible business buyers will seek to get the valuation and price reduced.
Other factors also come into play in most sales of small businesses. Sale price may well be linked to whether, as seller, you are prepared to accept any deferred payment, earn outs, to stay on in the business. All these issues can fundamentally impact business worth, as can tax efficiency on business sale for both buyer and seller.