The houses are the division of the sky into twelve pieces starting from the horizon of the place where you were born. They are not the signs: the signs divide the band of the zodiac, and the houses divide the sky as seen from one point on Earth, at one exact time.
The difference fits in one sentence. The sign says in what manner; the house says in what area. Mars in Aries describes a style; Mars in the 6th house says where that style shows up, at work, in the routine, in the body. A planet always has both, and they answer different questions.
That is why the house needs the birth time and the sign does not. The zodiac takes a month to change sign; the houses go all the way round once a day.
Two lines make the skeleton of the twelve houses. The Ascendant is the degree of the zodiac that was rising on the eastern horizon, and it is the cusp of the 1st house. The Midheaven is the highest degree at that instant, and it is the cusp of the 10th. The other eight come from dividing the space between those four points, and that is where the argument starts, because there is more than one way to divide.
This site uses Placidus, which divides the TIME each degree takes between rising and culminating, rather than the space. It is the most widely used system in the West, and it has a consequence almost no text mentions.
In Placidus, the size of a house depends on the latitude, and the further from the equator, the more unequal. Sweeping a whole day, this is the smallest and the largest house that appear at each latitude:
At 0.5° of latitude, the smallest house has 27.6° and the largest, 32.7°; at 15°, 25.3° and 36.2°; at 23.44°, 23.7° and 38.9°; at 30°, 22.3° and 41.6°; at 40°, 19.7° and 47.5°; at 50°, 16.3° and 58.1°; at 60°, 10.9° and 84.9°; and at 66°, 3.3° and 147.2°.
Near the equator the twelve are nearly level. At 60 degrees of latitude one house is eleven degrees and another is eighty-five, the same wheel, and one slice seven times the other. It is not a calculation error: it is what the definition of Placidus produces once the days stop lasting twelve hours.
If another site gave you a different house for the same planet, this is almost always why. The three most common systems put planets in different places, and the disagreement is not small:
In Belém, at 1.46° S, Placidus and equal houses disagree on 6.2% of the planets, and Placidus and whole sign on 51.3%; in São Paulo, at 23.55° S, 12.7% and 51.9%; in Lisbon, at 38.72° N, 23.9% and 53.4%; and in Berlin, at 52.52° N, 39.3% and 57.5%.
Between Placidus and whole sign, more than half the planets change house. That is not a disagreement about detail: it is the whole reading changing subject. And look at the other count, between Placidus and equal houses the disagreement grows with latitude, from 6.2% in Belém to 39.3% in Berlin, because it is the latitude that distorts Placidus.
None of the three is the right one. They are different conventions about where to cut, and each school defends its own. What an honest reading must do is say which system it used, and that is why this site's answer carries the system along with the chart.
Your chart comes with all twelve houses calculated, and the calculation is free.
See my housesThe houses turn a full circle every day, so getting the time wrong changes the planets' houses. Measured in São Paulo, across ten years of sky:
Getting the time wrong by 4 minutes, 3.2% of the planets change house, and 28.3% of the charts have at least one changing; by 15 minutes, 11.9% and 72.0%; by 30 minutes, 23.6% and 93.8%; and by 1 hour, 49.3% and 99.9%.
With an hour of error, 99.9% of charts have at least one planet in another house. Four minutes already move 28.3% of them, and four minutes is the difference between the delivery room clock and what somebody wrote down afterwards.
The signs, under the same error, barely move. That is why anyone who does not know the time still has a reliable reading of signs and has no reading of houses, and it is honest to know which of the two is being discussed.
A Placidus cusp is a fraction of the arc a degree travels between rising and culminating. Past 66.5619 degrees of latitude, which is 90 minus the tilt of the Earth, of 23.4381 degrees, there are degrees of the zodiac that never rise and never set at that place. The arc does not exist, and the calculation has no answer.
Measured, what comes out there is one house of zero degrees and another of three hundred and sixty: eleven houses squeezed into a corner and one swallowing the whole chart, with every planet inside it. That is not imprecision, it is a wrong answer wearing the face of a right one, which is the worst kind.
So above that line this site switches to equal houses, and says that it switched. Equal houses exist at any latitude, because they are a division of the ecliptic and not of the daily motion. The price is that the Midheaven stops being the cusp of the 10th and falls wherever it falls.
A house is not an area of life with a sharp border. The division is a convention, and the systems disagree in more than half of cases, anyone reading a house as if it were a fixed address is treating a choice of method as if it were a fact about the sky.
And a planet on the edge is a planet on the edge. If it sits one degree from the cusp, half an hour of difference in the recorded time puts it on the other side. The useful reading there is the one that mentions both houses, and not the one that fakes a precision the data does not have.
A limit said out loud, because it is part of reading seriously: none of this is prediction. Astrology describes tendency and gives vocabulary for what a person already lives, it does not determine what will happen, and nobody should be selling that.
And the questions that come up most on this subject, with the short answer:
What is the difference between a sign and a house? The sign is where the planet sits in the band of the zodiac; the house is where it sits in the sky as seen from the place you were born. The sign says in what manner, the house says in what area. A planet always has both.
Why did another site give me a different house? Almost always because it used another system. Between Placidus and whole sign, more than half the planets land in a different house; between Placidus and equal houses, from 6.2% to 39.3% depending on the latitude. This site uses Placidus and reports the system with the chart.
Do I need the exact birth time to have houses? You do. With fifteen minutes of error, 72.0% of charts already have at least one planet in another house; with an hour, 99.9%. Without the time you can read signs, and you cannot read houses.
Are all houses thirty degrees wide? In equal houses and in whole sign, yes. In Placidus, no: the size depends on the latitude, and at 60 degrees one house can be eleven degrees while another is eighty-five.
Which house system is the right one? None, and that is the honest answer. They are different conventions about where to cut, and there is no experiment that decides between them. What you can demand of a reading is that it says which one it used.
Which house is a planet on the cusp in? The one the calculation puts it in, but if it sits less than a degree from the edge, the answer depends on the time being right to the minute. There, a sensible reading mentions both houses.
In short:
Keywords astrological houses, first house, house system, Placidus, cusp
Between Placidus and whole sign, more than half the planets land in a different house. None of the systems is the right one, what an honest reading does is say which one it used. See your chart free here.
The twelve houses
Questions for people just starting out
The Sun in the 12 houses
The sign says how; the house says where. It is the piece that depends most on the exact time of birth.
Mercury in the 12 signs
Your Mercury is in your Sun's sign, the one before or the one after, and it is what explains why two people of the same sign think so differently.
Venus in the 12 signs
Your Venus is in your Sun's sign, in the two before it or the two after it, and it is what explains why two people of the same sign love so differently.
