Not only is it hard to remember speed limits in kilometers, but the French system has different limits for wet and dry conditions.
If it is less than two years since you passed your test, the lower wet weather limits apply at all times.
Dry Weather Speed Limits
• Built-Up Areas: 50 = 31 mph
• Outside Built-Up Areas: 90 = 55mph
• Dual Carriageways and Non-Toll Motorways: 110 = 68mph
• Toll Motorways: 130 = 80 mph
Wet Weather Speed Limits and new drivers
• Built-Up Areas: 50 = 31 mph
• Outside Built-Up Areas: 80 = 49 mph
• Dual Carriageways and Non-Toll Motorways: 100 = 62 mph
• Toll Motorways: 110 = 68 mph
See more on driving in France, including fines, here