Online sofa shopping can be tricky with unclear photos and nonreturnable policies, so educate yourself about size, fabric and construction before placing an order. Sofas from RH, such as the model shown above, come in multiple lengths and depths. (RH)

The promise of online shopping — that virtually anything you want can be sent to you within a day or two — is not true of many home items, and no item is it less true of than a sofa. Go to just about any furniture website and you will find that sofas have anywhere from a two-week to three-month lead time, which is a long period to wait when you want that sofa now.

Long lead times are a result of customization; most companies now sell only sofas that require some sort of customization — fabric choice, arm style, leg color and size, to name a few. And once ordered, your sofa decisions are set in stone; custom orders are nonreturnable.

Sofas with shorter lead times — and the possibility of returning them — do exist. Companies such as Crate and Barrel and RH (formerly Restoration Hardware) offer a limited range of “quick-ship” models. But those are upholstered in basic neutral fabrics and shipping (if the item is available in your Zip code) still takes a couple of weeks. If you are not satisfied, you can usually return a quick-ship sofa, but it has to be within a 30-day period (you need to contact Crate and Barrel within seven days) and you are often required to pay a restocking fee.

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Even if you remove the notion of getting your sofa quickly, the entire online sofa shopping experience is tricky; not only is the sofa likely to be one of the more expensive home purchases you make, it also needs to be comfortable, a highly subjective requirement that is truly only determined in person.

To successfully purchase a sofa online, you should educate yourself on a few matters.

Size: Your room will determine the sofa’s length; in general, your sofa should take up between ­one-third and one-half of the wall it sits against. Your physical height will dictate its depth: Taller people often prefer deeper sofas and shorter people prefer shallower. If your friend has a sofa that you think is comfortable, ask to take its measurements. Or test out sofas at a local furniture store and make note of the dimensions that are most comfortable for you. Most important, make sure you measure the interior space of your home’s doorways, passages and stairwells for delivery — that sofa won’t be of much use to you if it’s stuck on your front lawn.

Fabric: Online furniture companies typically offer free swatches, but there is usually a five- to 10-swatch limit. Fabric colors can vary from one computer screen to another, so it’s a good idea to order a swatch before completing your order.

Construction: When perusing online product descriptions, look for buzz words such as “eight-way, hand-tied steel springs” — those are the strongest and most resilient springs available. Frames should be made from “kiln-dried hardwood” and be “corner blocked” for stability. Also, look for “mortise and tenon” joinery. Sofa cushion inserts will usually be down, polyester or foam — or some combination of the three. To determine the stuffing that you find most comfortable, test out various fills at a local store.

I have assessed some of the most popular online furniture companies so that the market is easier for you to navigate. Here’s how their sofas stack up.

Best construction and quality: Serena & Lily

At Serena & Lily, you will find an edited selection of stylish sofas made with top-quality materials and excellent construction. Click on “Dimensions & Care” and you’ll see all the buzz words that signify quality and the sofa’s dimensions. Serena & Lily does not have a large fabric selection; pattern offerings include only stripes and checks. However, the fabrics it does have are stylish and of good quality. You can see how a fabric will look on a sofa by just clicking on a swatch. For some sofas, you will need to choose among three wood leg colors.

Serena & Lily sofas range from about $2,000 to $7,000, are made to order, have a six- to eight-week lead time and are nonreturnable.

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Best online experience: Crate and Barrel

Crate and Barrel’s website has clearly laid out product information that includes sections on dimensions, comfort, reviews and care. The section “How does it sit?” shows you how a sofa measures up in terms of comfort (cushion firmness, seat depth, height). Click on any fabric swatch and you can see how the finished sofa will look. The company’s iPhone app lets you use your camera to see how the sofa would look in your room. Its new Studio Series Customizable style requires that you choose your arm style, leg finish and fabric.

Most Crate and Barrel sofas range from around $1,500 to $3,300, are made to order, have a nine- to 11-week lead time and are nonreturnable. Quick-ship sofas typically come in one color and are usually delivered between seven and 14 days.

Best price range: Pottery Barn

All Pottery Barn sofas are custom-made and require you to choose size and fabric. For PB Comfort styles, customers choose arm style (roll or square), cushion fill (memory foam or down blend), back cushions (scattered pillows or box edge) and fabric. The company also offers many sleeper sofas. Unfortunately, the site does not let you see the sofa in every available fabric (only solids are viewable) and supplemental information is inconsistent. For some models, there is added photography including 360-degree views of the sofa and video content that explains construction, but for other models there is nothing more than the static frontal view. Pottery Barn sofas range from about $600 to $3,500, are made to order, have a four- to 12-week lead time and are ­nonreturnable.

Best fabric selection: Ballard Designs

Ballard Designs has the largest selection of fabrics and patterns (over 350!). Like other sites, you can see what your sofa will look like from one fabric to another, but Ballard warns that those digital images may differ in pattern placement from the actual item. The site also has detailed dimensions and comprehensive product information, but it’s a bit buried in the “Supply Your Own Fabric” section.

Ballard Designs sofas have a 12-week lead time and range from about $1,200 to $4,200. One thing to note: Your credit card will likely be charged in two payments: once for the fabric, once for the frame.

Best customizable sizing: RH

RH offers multiple length and depth options for its sofas as well as a choice between standard (polyfiber wrapped around foam core) or down-feather fill (down, feather and polyfiber wrapped around a foam core). RH’s fabric selection is edited to neutrals and solids, but there are many textures including linens, velvets and performance, stain-resistant fabrics. The company’s online language regarding its quick-ship program is a bit misleading; there are sofas that are ready for delivery within three to 10 days, but you have few choices. To see what’s available in your area, click on the “View In Stock Items” link. Just enter your Zip code and you will see the available sofas.

Sofas range from around $2,000 to $8,200 and have a four- to 12-week lead time. Custom orders begin production immediately and cannot be canceled, changed or returned. A nonrefundable 50 percent deposit is taken when the order is placed.

Mayhew, a “Today” show style expert and former magazine editor, is the author of “Flip! for Decorating.”

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