Ninety degrees, seven degrees of orb
A square is a quarter of the circle, 90 degrees of ecliptic longitude between two bodies, and the orb used on this site for a square is seven degrees. Mars anywhere from 83 to 97 degrees from Saturn qualifies, in either direction, since a square counts whichever body is ahead.
Because a full circle contains two squares to any fixed point, Mars squares Saturn twice in each of its roughly two year laps, once approaching the opposition and once leaving it. Saturn drifts only a few degrees during that time, so the pattern is close to regular. Each square holds within orb for a couple of weeks.
Squares also fall between signs of the same modality but different elements, which is where the friction is usually located. Mars in Aries square Saturn in Cancer puts a cardinal fire body against a cardinal water one. Both want to initiate, and they want incompatible things.
Force meeting structure
Mars in the tradition is the raw willingness to act, cut, compete and start. Saturn is the structure that says how, when and at what cost, along with the patience to see something through years after the excitement has gone.
A square is the aspect that forces the issue. Where an opposition produces awareness and a trine produces ease, a square produces movement through resistance, because the two bodies are close enough to interfere and too far apart to cooperate. Applied to this pair the classic description is delayed force: energy that meets an obstruction early, then either learns to work through it or stalls and turns bitter.
The older sources are frank about the unpleasant version, which they describe as anger held under pressure and a habit of self denial that goes past usefulness. The modern reading tends to emphasise the other outcome, which is stamina. Someone whose first attempts were consistently blocked often ends up with a working method rather than a talent, and that method is durable in a way that talent is not.
Sign, house and the strength of each end
The reading shifts a great deal depending on which body has the better position. Mars in Scorpio square Saturn in Leo gives a strong Mars against a Saturn that traditional dignity does not favour, and the friction reads as sustained pressure applied outwards. Reverse it, with Saturn in Capricorn or Aquarius against a Mars in Cancer or Taurus, and the description tips towards inhibition instead.
Houses tell you where the load sits. The tenth and first are the visible version, about career and how you present yourself. The fourth and seventh are domestic, and are often read as an early experience of authority that set the pattern.
Saturn's slowness matters for a different reason. It spends about two and a half years in each sign, so everyone born in that stretch shares a Saturn sign. What individualises the aspect is Mars, which moves quickly, and the house placement, which depends on birth time. Without a reasonably accurate time the house half of the reading is guesswork.
How tight is it, and what else is involved
Orb does most of the work. Inside two degrees the description above tends to be recognisable without prompting. Between four and seven it is a contributing factor among several, and it can be substantially reworked by a supporting aspect, for example a sextile from Jupiter to Mars.
Check whether the square is exact by degree or crosses a sign boundary, since an out of sign square, say Mars at 29 Taurus and Saturn at 2 Virgo, is still within orb but loses the modality logic that gives the aspect its usual shape. Many astrologers weaken the reading in that case.
The check above reports the exact separation, both signs and both houses, so you can see which version of this you have rather than reading a general account and hoping it fits.
Questions people ask about this
What orb is used for Mars square Saturn?
Seven degrees, which is the standard square orb here. That covers a separation of roughly 83 to 97 degrees. Inside two degrees the aspect is usually treated as a defining feature of the chart, and beyond five as a secondary note.
Does Mars square Saturn mean I will struggle?
No, and no aspect predicts an outcome on its own. The tradition reads this contact as effort meeting resistance, which some charts express as blocked frustration and others as unusual stamina. Sign, house, orb and the rest of the chart decide which.
How often does Mars square Saturn happen?
Twice in each Mars orbit of roughly two years, once on the way to the opposition and once on the way back. Each occurrence stays within the seven degree orb for about two weeks.
Is the square worse than the conjunction?
They are different rather than ranked. A conjunction fuses the two bodies so the restraint is built into the drive itself. A square keeps them separate and in conflict, which is more uncomfortable to live with but easier to notice and work on.
What is an out of sign square?
One where the degree separation is close to 90 but the two signs are not in square modality relationship, which happens near sign boundaries. The aspect still counts by orb, but most astrologers read it as weaker because the sign logic no longer supports it.
Do I need my birth time for this aspect?
Not for the aspect itself, since Mars and Saturn both move slowly enough that their separation barely changes across a day. You need the time for the houses, and the houses carry a large part of the interpretation.