Simply enter your mileage and petrol cost here.     Annual Mileage:  Current MPG:  Petrol cost (pence per litre):  LPG cost (pence per litre):        Your annual savings running on LPG.   Petrol Cost Per Annum:  LPG Cost Per Annum:  Saving Per Annum:    The calculations assume a 10% reduction in MPG when using LPG.