Gas Mark is a set of named oven settings, not a continuous formula like Celsius–Fahrenheit conversion. OvenTemp therefore uses one immutable fixture: 1 = 140 °C / 275 °F, 2 = 150 / 300, 3 = 165 / 325, 4 = 177 / 350, 5 = 190 / 375, 6 = 200 / 400, 7 = 220 / 425, 8 = 230 / 450, and 9 = 245 / 475. A lookup returns a row or returns no Gas Mark; it never invents a value between rows.
Read each row as one fixed triplet
The supported rows are exactly: GM1 140 °C / 275 °F; GM2 150 / 300; GM3 165 / 325; GM4 177 / 350; GM5 190 / 375; GM6 200 / 400; GM7 220 / 425; GM8 230 / 450; GM9 245 / 475. These values are curated lookup data. Do not derive one column from another and expect identical rounded results; use the complete published row when a recipe names its Gas Mark.
No quarter marks, half marks, Gas Mark 10, or interpolation
OvenTemp does not support Gas Mark 1/4, 1/2, 10, or any other row outside the published fixture above. It also does not infer that a temperature halfway between two rows must be a half mark. Such notation varies across references and appliances, while an interpolated answer can look more authoritative than it is. An unsupported input remains unsupported, and the interface directs the cook back to the recipe or appliance instructions.
Keep the published row distinct from recipe shorthand
The common shorthand “180 °C / 350 °F / Gas Mark 4” is useful in recipe conversation, but the published Gas Mark 4 row in OvenTemp is 177 °C / 350 °F. That distinction is intentional. Similarly, 200 / 400 / GM6 and 220 / 425 / GM7 happen to align with the curated row values. Always label whether you are quoting an exact formula, a fixed Gas Mark row, or a rounded recipe grouping.