Thunderpants Sizing Guide: How to Measure Yourself at Home

Quick answer

To get your Thunderpants size, measure your waist at the narrowest point and your hips at the fullest point using a soft tape measure. Write both numbers down in centimetres and compare them to the Thunderpants size chart for the specific style you want. If you are between sizes or prefer a looser fit, size up; for a snug fit, size down. For swimwear, stick to your usual underwear size.

Buying underwear online can feel like a gamble, especially when you cannot try before you buy. The good news is that Thunderpants sizing is straightforward once you know your measurements. This guide walks you through measuring yourself at home, reading the Thunderpants size chart, and choosing the right size for different styles.

We will also cover how to measure for underwear, what to do if you are between sizes, and how Thunderpants swimwear and kids' sizes compare. By the end, you will have the confidence to order the right size the first time.

How to measure your waist and hips at home

You will need a soft tape measure and a mirror or a helpful friend. Wear lightweight clothing or your usual underwear. Stand up straight with your feet together and breathe normally. To find your waist, locate the narrowest part of your torso, usually just above your belly button. Wrap the tape around your body, keeping it parallel to the floor. It should be snug but not tight enough to leave marks. Write down the number in centimetres.

For your hips, find the fullest part of your bottom, usually about 20 cm below your waist. Wrap the tape around the widest point, again keeping it level. Make sure the tape is not twisted at the back. Record this number too. If you are measuring for a child, use the same method but check their current clothing size as a starting point. Always measure over underwear, not bulky clothing.

• Measure in centimetres for easiest comparison with Thunderpants size charts.
• Keep the tape snug but not tight; you should be able to slip a finger underneath.
• Measure twice to confirm your numbers.

Reading the Thunderpants size chart

Thunderpants provides size charts for each product category, but the core measurements are waist and hip. For women's underwear, sizes typically range from 8 to 20 (NZ/AU) or XS to XXL. For men's, sizes are usually S to XXL. Kids' sizes are based on age and weight. Always check the specific product page because some styles, like the Everybody Boxer, are designed to fit all genders and may have a unisex size chart.

If you are between sizes, consider the fabric and cut. Bamboo styles like the Everybody Boxer have stretch and may feel more forgiving, while 100% cotton drill items like napkins are not worn on the body. For underwear, if your waist and hip measurements fall into different sizes, choose the size that matches your hip measurement for bottoms, as hips are usually the widest point.

• Check the individual product page for the most accurate size chart.
• For unisex styles, follow the size chart provided for that product.
• When in doubt, size up for comfort.

Special considerations for swimwear and kids

Thunderpants swimwear is designed to fit like underwear, so you should stick to your usual underwear size. The High Waist Swim Pant Popeye, for example, uses a durable nylon/spandex fabric that holds its shape in water. If you are between sizes in swimwear, you might prefer to size up for a less restrictive feel, but keep in mind that swim fabric can relax slightly when wet. For kids, the Original style is designed to be waist-high in small sizes, making it great for toilet training, while the Boxer style has extra room in front and is available in school-aged sizes.

Kids' sizes are based on age and weight, but every child is different. If your child is in between sizes, consider their build and how they like their underwear to fit. The Kids Original Plain Black is modest and comfortable for active play, while the Kids Boxer Plain Black offers a bit more room. Both are made from fairtrade organic cotton, which is soft and breathable.

• For swimwear, order your usual underwear size.
• For kids, use age and weight as a guide but check the size chart.
• Pre-schoolers may prefer the Original style for toilet training.

What to do if you are between sizes

If your measurements fall between two sizes, think about how you like your underwear to feel. For a snug, supportive fit, choose the smaller size. For a relaxed, roomier fit, choose the larger size. If you are buying bamboo underwear, remember that it has natural stretch and may feel more forgiving. For cotton styles, there is less give, so sizing up might be more comfortable. If you are still unsure, check the product description for fit notes or reach out to customer service.

Another tip: look at the model's size in the product photos if available. Many online stores list the model's measurements and the size they are wearing. This can give you a real-world reference. Also, read customer reviews for fit feedback. If many reviewers say a style runs small, consider sizing up.

• Size down for a snug fit, size up for a relaxed fit.
• Bamboo styles have more stretch than cotton.
• Check model info and reviews for extra guidance.

Decision rules for choosing your Thunderpants size

• If your waist and hip measurements fall into different sizes: For bottoms, choose the size that matches your hip measurement, as hips are the widest point and determine comfort. Hips rule for bottoms.
• If you are between sizes and prefer a snug fit: Size down, especially for cotton styles that have less stretch. For bamboo styles, you might still be comfortable in the smaller size. Snug = size down.
• If you are between sizes and prefer a relaxed fit: Size up. This is also a good idea if you are buying swimwear and want a less restrictive feel. Relaxed = size up.
• If you are buying for a child: Use age and weight as a guide, but check the size chart. For toilet training, the Original style is designed to be waist-high in small sizes. Kids: check chart, consider style.
• If you are still unsure: Check the product page for fit notes, model measurements, and customer reviews. When in doubt, size up for comfort. When in doubt, size up.

Thunderpants styles and sizing notes

• Everybody Boxer Powder Pink Bamboo: Made with organic bamboo elastane, it's breathable, comfy and moves with you, suitable for all genders. Because there is no cotton, these have amazing drying and wicking properties. The stretchy bamboo fabric offers a forgiving fit, so if you are between sizes, you may find the smaller size still comfortable.
• High Waist Swim Pant Popeye: Constructed in very durable nylon/spandex. Stick to your undies size when ordering. Thunderpants recommends ordering your usual underwear size for swimwear, so use your measured size from the chart.
• Kids Original Plain Black: Designed to be waist high in the small size for wee kids which makes them excellent toilet training pants. As the sizes get bigger the waist lowers a bit. For younger children, the high waist provides extra coverage; older kids get a more standard fit as sizes increase.
• Kids Boxer Plain Black: Super comfy with a bit of extra room in the front and no double layer gusset. Only available in school aged sizes. If your child is in school, the Boxer style offers more room; for pre-schoolers, the Original style is recommended.

Who this sizing guide is for

Best for

• Shoppers buying Thunderpants online for the first time
• Anyone between sizes who needs help deciding
• Parents choosing underwear for children

Not for

• People who already know their exact Thunderpants size and prefer no guidance
• Those looking for a style not covered by waist and hip measurements, such as accessories

With a soft tape measure and a few minutes, you can find your Thunderpants size without the guesswork. Measure your waist and hips, check the size chart for your chosen style, and use our decision rules to settle any between-size doubts. That way, your first order is more likely to fit well and feel comfortable from day one.