Running T-shirt Sizes: How Do You Choose Between Two Sizes?

If you're unsure which size running T-shirt to choose, compare your measurements to the size chart and to a piece of athletic wear that already fits you well. Then choose based on the amount of room you need at the shoulders, chest, and under the arms. Always going up a size doesn't guarantee a better fit.

Use a garment you already know works

Take out a top you like to wear for running. Lay it flat and note the relevant measurements: width under the armholes, back length, and—for long sleeves—sleeve length. Follow the measurement method specified in the brand’s guide, if one is provided.

Be careful not to confuse body measurements with garment measurements. A chest circumference and the width of a T-shirt laid flat are not interchangeable values. If the size chart lacks precision, ask how to interpret it before ordering.

Determine the desired fit

A top intended for quick workouts may be worn differently than a garment chosen for a leisurely outing. Wearing a sports bra, a base layer, or a bag also changes how it feels. Try on the garment with the items you’ll actually be wearing.

Don’t rely solely on the letters S, M, or L. Sizes vary by model and brand. Always use the product guide for the item you ordered as your reference.

Try three movements before deciding

Raise your arms, lean slightly forward, and mimic your running stride. The garment should allow you to perform these movements without having to readjust it each time. Check the collar and underarms, which may seem comfortable when you’re standing still.

The Isard T-shirt product page indicates a sporty fit and recommends your usual size. This recommendation is a starting point; your preferred level of comfort and your measurements will help you refine your choice. If you’re unsure, share this information with our customer service team.

Placing a Custom Order

Size deserves special attention before adding a first name or logo. Personalization changes the return policy listed on the relevant product pages. Be sure to review these terms and confirm the fit before proceeding with customization.

For a group, avoid simply asking, “What size do you wear?” Provide the exact size guide, have everyone take their own measurements, and compile the responses before finalizing the order. This approach minimizes discrepancies between standard clothing sizes and athletic sizes.

Frequently Asked Questions

Do you need a tight-fitting T-shirt for running?

No. The fit should match your preference and the intended use of the product. A form-fitting garment isn’t automatically compression-style.

Should I choose a different size for short-sleeve versus long-sleeve shirts?

Consult both size guides. Be sure to check the sleeve length and shoulder room, and don’t assume that all cuts are identical.

Where can I compare styles?

Browse the running tops in the store. Open the product page for each model you’re considering and compare its size guide before choosing your size.