Ninety degrees, and how the pair gets there
A square is ninety degrees with an orb of about seven. Venus and Mars form squares twice in each of their roughly two year cycles, once while separating from conjunction and once while closing back towards it, so this angle occurs more often than either the conjunction or the opposition.
Both planets change speed considerably. Venus can be moving over a degree a day or standing still at a station. Mars ranges from about three quarters of a degree a day down to a crawl. The result is that some squares pass in under a week and others hold for a month, which means the number of charts carrying a given square varies a lot.
The two bodies sit in signs of the same mode and different element. Cardinal squares between them argue about what to start, fixed squares about what to keep, mutable squares about what to change.
Friction between two appetites
Venus stands for attraction and preference, Mars for the drive that acts on it. In most configurations these cooperate at some distance. A square makes cooperation conditional on effort, so wanting something does not automatically produce a sensible way to pursue it, and pursuing something does not automatically respect what made it attractive.
The classic descriptions of this aspect are about intensity and misjudged timing in equal measure. Astrologers associate it with people who are rarely lukewarm, who put real force behind their preferences, and who find that the force sometimes damages the thing it was aimed at. It appears frequently in the charts of working artists, on the reading that dissatisfaction with your own output is what keeps you producing more of it.
None of that is a verdict. A square is a demand for action, and demands can be met well or badly. What the aspect describes is the absence of an easy route between preference and pursuit, not a prediction about where the difficult route ends up.
Which planet has the advantage
Look at the signs before you read anything else. Venus in Taurus square Mars in Leo is a square where Venus has the stronger footing and taste tends to win the arguments. Mars in Scorpio square Venus in Leo reverses that, and appetite sets the terms.
Where neither planet is well placed by sign, the square usually shows as a longer period of trial and error before the person finds a working arrangement between the two. That is one of the more consistent observations in the literature, and it is a claim about interpretation rather than astronomy, so treat it as a tradition rather than a finding.
Orb, stations and the useful checks
Inside three degrees this square is a strong feature. Between three and seven it is real but frequently subordinate to something else. A square that crosses a sign boundary breaks the shared mode and becomes a much weaker contact, whatever the degree count says.
Speed is worth checking. If either planet was near a station at your birth, it was barely moving, which most astrologers read as a strengthening of that planet's part in the aspect. A stationary Mars square a fast Venus is not the same as the reverse, even at an identical orb.
Also check for anything reaching both ends. Saturn touching either planet tends to formalise the square and slow it down. Jupiter tends to enlarge it without resolving it. The check above reports the orb, both signs and houses, and whether either body was retrograde, which together tell you which version of this square you actually have.
Questions people ask about this
Is Venus square Mars a bad aspect?
The tradition treats it as difficult, meaning it asks for effort rather than granting ease. That is not the same as harmful. Squares are consistently associated with productivity, and the outcome depends on sign, house and the rest of the chart.
How often does this square occur?
Twice in each Venus and Mars cycle of roughly two years, once separating from conjunction and once approaching the next one. The width of each window varies with how fast the two planets are moving at the time.
Do the two planets share a mode?
With a clean square, yes. Both sit in cardinal, fixed or mutable signs of different elements. A wide square that crosses a sign boundary loses that, and with it most of the logic behind the standard interpretation.
Is this aspect about sexual tension?
That is one common reading and it is narrower than the aspect. Venus and Mars cover attraction and assertion generally, so the square shows up in creative work, spending, competition and taste as readily as in anything sexual.
What does a retrograde planet do to it?
Mars retrograde is read as assertion turned inward, which usually makes the square less visible from outside and more of an internal argument. Venus retrograde is read similarly for the preference half of the pair.
How do I tell which planet dominates?
Compare their sign placements and their speed. A planet in its own sign, or one that was close to stationary at birth, is generally read as the stronger voice in the aspect. Both figures are shown in the check above.