There’s a slight snag with shopping online for clothes – you’re never quite sure if they’re going to fit. Companies have been trying everything from 3D models to augmented reality to solve the problem, but Stockholm startup Virtusize thinks it has a better way.

Virtusize asks shoppers to compare the size of a garment they want to buy with a garment they already own. By punching in that garment’s measurements into Virtusize’s Web app, which is hosted on partner shopping sites, shoppers get a visual representation of how well the desired item will fit. Virtusize’s logic is that a tape measure on an item of clothing is a more accurate representation of how well something will fit than measuring body shape.

Alternatively, shoppers can indicate to Virtusize that they already own a particular garment from a certain store and of a certain size, so the app can use that as a point of reference. Virtusize overlays the size of the shopper’s currently owned garment on top of the desired item, all in a very snazzy interactive graphic.

The 18-month-old company has partnered with 20 shopping sites in Scandinavia, Austria, Germany, and the UK, but they’ve also started talks in the US, which they say is a major target. Its ambition is to be the global standard for size and fit on fashion ecommerce sites and platforms.

Peder Stubert, one of the 10-person company’s five co-founders, said today that Virtusize is focusing squarely on the size and fit of clothing, not design. Clothing sizes vary dramatically across markets and between brands, he noted, and there is no universal standard. The company’s CEO, Gustaf Tunhammar, came up for the idea for Virtusize after being frustrated by having to frequently returns T-shirts he bought online that didn’t fit.

Clothing returns are costly for retailers. Not only are there the inherent postage and handling costs, but often the returned items have to go straight onto the discount rack, because they go out of season.

Technology companies have been trying to solve the online fitting conundrum in many ways, including with full-body scanners, digital avatars, and robotics. One of Virtusize’s major competitors is Boston’s True Fit, which uses data-driven algorithms to calculate a customer’s size and shape, according to the Wall Street Journal. It recommends a size for each garment and describes how it fits around the bust and hips. Because True Fit is secretive about how it does its calculations, it is difficult to assess how successful and scalable its method will prove to be. Other competitors include Clothes Horse and Fits.me.

Stubert believes Virtusize’s approach is very scaleable. It relies on getting measurement information for each garment from retailers or brands, which is then fed into Virtusize’s system. Each garment is then visually outlined within the app whenever a shopper clicks on the Virtusize button within a product page. The 2D approach is also preferable to 3D models, Stubert argued, because 3D can sometimes hide how tight or loose a piece of clothing might hang on the body.

Virtusize raised an undisclosed seed round from Swedish investment firm Öresund and angel investors, including a former eBay executive. Its biggest partnership is with Nelly.com, a leading online retailer in Sweden.