A narrow waist and wide hips in the same trousers
Short answer: Buy for the hip and have the waist taken in. Trousers with a high waist and elastane close the gap without alterations.
Why trousers gape at the back
If the trousers fit over the hip, the waistband is usually several centimetres too big at the waist. A gap appears at the back when you sit down. That is not a fault in the trousers, it is the difference between two measurements on your body.
The simplest route
Buy by hip measurement and have an alterations shop take the waistband in at the back. It is a cheap change that takes half an hour and makes the trousers a completely different garment to wear. See bamboo trousers for women.
Cuts that solve it themselves
Trousers with a wide, soft knitted waistband and a few percent elastane follow both measurements without alteration. So do leggings and sweatpants with a wide waist. See bamboo leggings and bamboo sweatpants for women.
Underwear by the same rule
Choose briefs by the hip too. A high waisted style follows the narrow waist without cutting over the hip. See bamboo briefs for women.
Frequently asked questions
Should I buy for the waist instead
No. Trousers that pull over the hip never become comfortable, while a loose waist can be fixed.
What does taking in a waistband cost
It is among the cheapest alterations available and it lasts for years.
Is a belt a solution
It holds the trousers up, but the gap at the back is still there.