ΔE 8.3, close: similar, with a visible difference side by side. Burnt Umber is a little lighter, more muted, cooler than Sepia.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Burnt Umber is a little lighter, more muted, cooler than Sepia.
The same difference applies the other way round: Sepia is a little darker, more saturated, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Sepia on the colour wheel See Burnt Umber on the colour wheel
All matches: Sepia equivalents · Burnt Umber equivalents