The diameter of headband is 16cm , can be stretched up to 23cm around. If run large, you can adjust the size by sewing it.

Specifications:
Product name: sleep mask
Bluetooth Specifications: V5.0+EDR/A2DP/AVRCP/HFP
Frequency range: 2.4026GHz-2.480GHz
Transmission distance: more than 20 meters
Channel: Stereo
Speaker parameters: 24 ohms/30mm
Speaker power: 10mW x2
Signal-to-noise ratio: 104dB
Function: previous song, next song, volume up, volume down, play, pause, answer a call, make a call, activate SIRI, microphone intercom
Playtime: 6 hours (tested at 100% volume on iPhone)
Talk time: more than 7 hours
Standby time: more than 260 hours (actual test)
Charging time: about 1.5 hours

Features:
1* COMFORTABLE KIDS HEADPHONES: Headband headphones are a great choice for girls and boys of any age who hate earbuds or struggle with bulky in-ear headphones. The cute headband is fun to wear, washable, and compatible with most devices.
2*HEARING PROTECTION VOLUME LIMIT: The headband is soft and washable, and the slim speaker is limited to 104dB to protect small ears. There are no earbuds that stick in your ears, or bulky headphones that don't fit.
3*Children's Headphones for School and Travel: The comfortable and elastic headband stays in place and won't interfere with car seat headrests or airplane seats, allowing your child to sleep comfortably while traveling.
The thin speaker and Bluetooth wireless are compatible with most phones, tablets, laptops and other devices.
4*Children's Headband Earphones: Kids will love these characters and colors and won't be bothered by inappropriate earbuds. You can also pull them over your eyes as a nap time sleep mask!

Packing list:
1 Bluetooth compatible headset
1 scarf
1 x USB charging cable
1 x Description
1 OPP bag

Note: The color deviation is subject to the actual system configuration.