Warmth around a wound can mean two quite different things, and which one applies depends on whether it is new.
As a sign to report. Redness, increased warmth, or swelling around the wound are signs of infection for venous ulcers, ischemic ulcers and diabetic foot ulcers alike. For a pressure sore, the sign is skin close to the sore that is warm or swollen. With cellulitis, warm skin in the area of redness is one of the symptoms.
Increased, in three of those. The point is not a temperature but a change.
As an ordinary feature. With venous ulcers, the surrounding skin may be shiny, tight, warm, or hot, and discolored. That is one of the signs and symptoms of the ulcer itself, not one of the reasons to call. So on a leg with a venous ulcer, warmth may already be part of the picture.
There is a third case worth knowing, from the opposite direction. With ischemic ulcers, when you raise the leg, it turns pale and cool to touch. For a leg short of arterial blood, coolness rather than warmth is the finding.
There’s no set threshold for this, and no way to measure it precisely at home. Hands are not thermometers, and comparing one limb against the other is the closest most people can get.
That is why the useful report is comparative and specific: warmer than it was yesterday, or warmer than the other leg, rather than simply warm.