Working it out by hand
1 acre is 43,560 sq ft and 1 guntha is 1,089 sq ft. Turn the acre into square feet first, then into guntha. For 2.5 acre:
2.5 acre × 43,560 ÷ 1,089 = 100 guntha
1 एकड़ = 40 गुंठा। “2 एकड़ 15 गुंठा” = 2 × 40 + 15 = 95 गुंठा।
Measured the plot with a tape instead? Use the plot area calculator.