Pressure ulcers are measured using a combination of linear dimensions (length, width, and depth in centimeters), wound bed assessment, and staging. The standard approach orients the wound like a clock, with the patient’s head at 12 o’clock, and takes perpendicular measurements at the longest and widest points. This consistent method lets clinicians track whether a wound is healing or getting worse over time.
Length, Width, and Depth
The foundation of pressure ulcer measurement is three linear dimensions, all recorded in centimeters. Length is measured head to toe at the wound’s longest point. Width is measured side to side at the widest point perpendicular to the length, so the two lines form a “+” shape. Depth is measured at the deepest point of the wound bed.
For depth, a sterile cotton-tipped applicator is gently inserted into the deepest part of the wound. The applicator is then pinched or marked at the level of the surrounding skin, removed, and measured against a ruler. This gives a straightforward depth reading, though some patients find probing uncomfortable, so gentle technique matters.
Consistency is critical. Every person measuring the wound should use the same orientation (head at 12 o’clock, feet at 6 o’clock) and the same landmarks. If one clinician measures diagonally and another measures head to toe, the numbers won’t be comparable, and you lose the ability to track progress.
Detecting Tunneling and Undermining
A pressure ulcer doesn’t only affect the visible surface. There can be significant hidden damage beneath intact-looking skin. Two types of hidden extension need to be checked: tunneling and undermining.
Tunneling (also called a sinus tract) is a narrow channel that extends in any direction from the wound base, like a tube burrowing into tissue. Undermining is a broader open area that spreads under the skin along the wound’s edges, like a shelf or cave. Both are detected by gently inserting a sterile applicator along the wound margins and feeling for spaces where the probe slides under intact skin.
Location and extent are documented using the clock method. If undermining runs from the 2 o’clock to 5 o’clock position and extends 3 centimeters under the skin, that gets recorded precisely. Tunneling is noted by its clock position and the depth of the tract. These hidden cavities can be substantial, so checking for them at every assessment prevents underestimating the wound’s true size.
Staging the Wound
Staging classifies how deep the tissue damage goes and is separate from the size measurements. The system, developed by the National Pressure Injury Advisory Panel, uses four numbered stages plus two additional categories.
- Stage 1: Intact skin with a non-blanchable red area. When you press on it, it doesn’t turn white. On darker skin tones, this may appear differently, so temperature and firmness changes help confirm it.
- Stage 2: Partial-thickness skin loss exposing a pink or red, moist wound bed. It may look like an open blister or a shallow crater. The wound bed is viable tissue, not dead.
- Stage 3: Full-thickness skin loss where fat may be visible, but bone, tendon, and muscle are not exposed. Areas with very little fat tissue, like the bridge of the nose, ear, and the bony bump of the ankle, cannot develop Stage 3 injuries because there’s no subcutaneous fat layer there.
- Stage 4: Full-thickness tissue loss with exposed bone, tendon, or muscle. These are the deepest wounds and often include tunneling or undermining.
- Unstageable: The wound base is covered by slough (yellow or cream-colored dead tissue) or eschar (dry, black, hard dead tissue) so the true depth cannot be determined. One exception: stable, dry eschar on the heel should not be removed just for staging purposes.
- Deep tissue pressure injury: Intact or non-intact skin with a localized area of persistent deep red, maroon, or purple discoloration. This signals damage in deeper tissue layers. These wounds may rapidly break down and reveal their full extent, or they may resolve without tissue loss.
A wound can only be staged at its worst. If a Stage 4 ulcer starts healing, it’s still documented as a Stage 4 that is improving. You don’t “reverse-stage” it to Stage 3 as it fills in.
Assessing the Wound Bed
Beyond dimensions and staging, describing what’s actually in the wound bed tells you whether healing is progressing. Four main tissue types are evaluated.
Healthy granulation tissue is pink and slightly bumpy, signaling that new tissue is forming. Dark red granulation tissue that bleeds easily on contact often signals infection or a stalled healing process. Excess granulation, where tissue mounds up above the wound surface, can also indicate problems.
Slough is cream or yellow dead tissue that may be loosely or firmly attached. Eschar is dry, black, hard necrotic tissue. Both types prevent healing by blocking new tissue growth. The amount of necrotic tissue or slough present is typically graded from absent to excessive. Epithelial tissue, which appears as new pink skin growing inward from wound edges, is a sign of late-stage healing.
Recording the percentage of the wound bed covered by each tissue type gives a useful snapshot. A wound that was 80% slough-covered two weeks ago and is now 60% granulation tissue is clearly improving, even if the dimensions haven’t changed much yet.
Evaluating Drainage
Wound drainage, or exudate, is assessed by type and amount. The volume is typically categorized as none, light, moderate, or heavy, based on what you see after removing the dressing. Light exudate dampens the dressing slightly, while heavy exudate may soak through it entirely.
The character of the drainage matters too. Clear or straw-colored fluid (serous) is normal during healing. Pink or light red fluid (serosanguinous) contains some blood and is common in the early stages. Thick, opaque, or foul-smelling drainage (purulent) suggests infection and warrants prompt attention. Documenting the color, consistency, odor, and approximate amount creates a baseline for spotting changes.
Checking the Surrounding Skin
The skin around the wound, called the periwound area, provides important clues about whether the wound is stable or worsening. Key signs to look for include maceration (skin that appears white, swollen, and waterlogged from excess moisture), redness and warmth that may signal spreading inflammation, hardness or firmness under the skin (induration), and any blistering or erosion at the wound edges.
Rolled or thickened wound edges can indicate a wound that has stalled, with the skin curling down instead of migrating across the wound bed. Periwound maceration is also associated with higher pain levels during dressing changes, so addressing excess moisture can improve comfort. The periwound area typically extends about 4 centimeters from the wound edge, and any changes in this zone should be noted.
Tracking Healing With the PUSH Tool
The Pressure Ulcer Scale for Healing, or PUSH tool, is a standardized scoring system that combines three measurements into a single number you can track over time. It evaluates wound surface area (length times width), exudate amount, and wound bed tissue type. Scores range from 0 to 17, with higher numbers indicating a worse wound and 0 representing a fully healed surface.
The advantage of the PUSH tool is simplicity. By plotting scores on a graph at each assessment, you get a visual trend line showing whether the wound is improving, stable, or deteriorating. A score that drops steadily over several weeks confirms that the current treatment plan is working. A score that plateaus or climbs signals something needs to change.
How Often to Measure
Federal guidelines for long-term care facilities call for daily monitoring of pressure ulcers, with full documented measurements at least weekly or with each dressing change. More frequent documentation is needed when complications appear or wound characteristics change. Each formal assessment should record location, stage, dimensions (including any tunneling or undermining), exudate type and amount, wound bed tissue type, pain, and the condition of surrounding skin.
Weekly measurements are generally sufficient for tracking healing trends. Daily monitoring between formal assessments focuses on spotting new problems early: increased pain, changes in drainage, new odor, or expanding redness around the wound.
Digital Measurement Tools
Digital wound measurement systems are becoming more common and offer advantages over manual ruler-based methods. These devices use technologies like stereophotogrammetry and structured light to create three-dimensional reconstructions of the wound, calculating area, depth, and volume from photographs.
Systems like Silhouette and similar 3D cameras can capture wound volume, which a simple ruler cannot. However, accuracy varies. Some devices have been found to overestimate wound volume compared to direct fluid displacement methods. Newer prototypes show better agreement, with area measurements from 3D cameras correlating well with traditional tracing methods. For most clinical settings, consistent manual measurement with a disposable ruler remains the standard, but digital tools add value for complex wounds where volume tracking matters or where multiple clinicians need to compare assessments across locations.