Reference Tables & DNA Notes

Notes and tables on generation size, cousin relationships and DNA Calculations

How Many Ancestors Could You Have?

GenerationRelationshipSize of Generation
1Self1
2Parents2
3Grand-parents4
4Great-grandparents8
52nd Great-grandparents16
63rd Great-grandparents32
74th Great-grandparents64
85th Great-grandparents128
96th Great-grandparents256
107th Great-grandparents512
118th Great-grandparents1,024
129th Great-grandparents2,048
1310th Great-grandparents4,096
1411th Great-grandparents8,192
1512th Great-grandparents16,384
1613th Great-grandparents32,768
1714th Great-grandparents65,536
1815th Great-grandparents131,072
1916th Great-grandparents262,144
2017th Great-grandparents524,288
2118th Great-grandparents1,048,576
2219th Great-grandparents2,097,152
2320th Great-grandparents4,194,304
2421st Great-grandparents8,388,608
2522nd Great-grandparents16,777,216
2623rd Great-grandparents33,554,432
2724th Great-grandparents67,108,864
2825th Great-grandparents134,217,728
2926th Great-grandparents268,435,456
3027th Great-grandparents536,870,912
3128th Great-grandparents1,073,741,824
3229th Great-grandparents2,147,483,648
3330th Great-grandparents4,294,967,296
3431st Great-grandparents8,589,934,592
3532nd Great-grandparents17,179,869,184
3633rd Great-grandparents34,359,738,368
3734th Great-grandparents68,719,476,736
3835th Great-grandparents137,438,953,472
3936th Great-grandparents274,877,906,944
4037th Great-grandparents549,755,813,888
4138th Great-grandparents1,099,511,627,776
4239th Great-grandparents2,199,023,255,552
4340th Great-grandparents4,398,046,511,104
4441st Great-grandparents8,796,093,022,208
4542nd Great-grandparents17,592,186,044,416
4643rd Great-grandparents35,184,732,088,832
4744th Great-grandparents70,368,744,177,664
4845th Great-grandparents140,737,488,355,328
4946th Great-grandparents281,474,976,710,656
5047th Great-grandparents562,949,953,421,312

  • Scientists estimate that there have been 7,500 generations since homo sapiens first evolved.
  • Only 107 billion people have ever lived on earth. This number is smaller than the number of 35th Great-grandparents if each person was unique.
  • In 2020 world population is approaching 8 billion. In 1000 world population was estimated at 275,000,000.
  • Going back 50 generations at an average of 30 years per generation puts 47th Great-grandparents birth year at about 500. World population at that time was estimated at less than 200 million, not nearly the 500 trillion needed to fill out a unique tree.
This problem is explained through pedigree collapse. At some point in every family tree related individuals will have children. Most researchers will find pedigree collapse beginning within 10 generations. If first cousins married, like Richard Hugh Sisson and Eliza Jane Cralle, their children would not have the usual eight Great-grandparents but instead only six beacause one set would be shared. The total possible number of ancestors in every generation going back decreases by 25%. The number of possible 10th great-grandparents for their children would drop from 4,096 to 3,072, and that is if there are no other instances of related individuals in that line reproducing. Instances of first cousins marrying becomes even more frequent as lines are traced back to royalty and nobilty when marriages to close famliy members were used to keep titles and land in the family. In researching genealogy on the Northern Neck of Virginia pedigree collapse is most often in relationships more distant than 3rd cousins. Many of those relationships were likely unknown and the result of a being in a small and somewhat isolated geographic area with a low population. Any family tree eventually will stop fanning out ▼ and will instead begin converging into a diamond shape ◆. Some statisticians have estimated going back 30 generations for an Enlishman would result in 952 thousand unique ancestors out of an estimated population of 1.1 million instead of the possible 536 million which is obviously impossible.

Shared DNA in Ancestors

Relationship Shared DNA (%) Average Centimorgans Centimorgan Range
Self 100.00 7074 6800-7200
Parent 50.00 3485 2376-3720
Grandparent 25.00 1754 984-2462
Great-grandparent 12.50 887 485-1486
2nd Great-grandparent 6.25 420 186-713
3rd Great-grandparent 3.125 221 33-471
4th Great-grandparent 1.5625 122 14-353
5th Great-grandparent 0.78125 73 0-234
6th Great-grandparent 0.390625 48 0-192
7th Great-grandparent 0.1953125 36 0-166
8th Great-grandparent 0.09765625 27 0-98
9th Great-grandparent 0.048828125 22 0-93

Each person's DNA makeup is composed of one half of each of their parent's DNA. The DNA that parents pass on to their children is a random sampling. That means that while on average you share 25% of your DNA with each grandparent, that number can vary. It is highly unlikely not to share any DNA with a grandparent - the odds are about 1 in 8.4 million.

Most DNA testing is for autosomal DNA - this looks at the first 22 of a person's 23 chromosones and can find connections along any lineage. Y-DNA tests can only be taken by men to look at the Y chromosone, this information is passed father to son and means males are always guaranteed to share DNA with their paternal grandfather. Alternatively mitochondrial DNA or Mt-DNA is passed down by mothers to their daughters and sons. Anyone can take Mt-DNA tests because both sexes have mitochondrial DNA that is inherited from their mother's, mother's, mother, etc. This means that men and women are both guaranteed to share DNA with their maternal grandmother.

Most DNA testing companies report shared DNA in centimorgans (cm), a unit of measure that describes the size of DNA segments you have in common with another person. Total centimorgans may include one long segment of identical DNA or several tiny segments. Each DNA company tests and measures in a slightly different way so conversions from centimorgans to precentages is not exact.

DNA Genealogy is an interesting tool for family history researchers but the trail fades out faster than many realize. By the time you are looking at 5th Great-grandparents you are already statistically sharing less than 1% of their DNA. If two 6th cousins (who share 5th great-grandparents) compared DNA there would be only a 10% chance that they would share any DNA. By comparison 4th cousins have a 69% chance of sharing DNA and with 2nd cousins there is a 100% percent chance of shared DNA.

Cousin Calculation chart with DNA estimates

This chart can calculate relationship of two individuals with a known common ancestor. The percentage is the expected shared DNA for that relationship. Hover a box to see the average shared DNA in centimorgans and the range of centimorgans.

Person 2's relationship to common ancestor
Person 1's relationship to common ancestor
  Parent Grandparent Great-grandparent 2nd Great-grandparent 3rd Great-grandparent 4th Great-grandparent 5th Great-grandparent 6th Great-grandparent 7th Great-grandparent 8th Great-grandparent 9th Great-grandparent
Parent Sibling
50%2613cm
1613-3488		 Niece/Nephew
25%1740cm
1201-2282		 Great Neice/Nephew
12.5%850cm
330-1467		 2nd Great Neice/Nephew
6.25%420cm
186-713		 3rd Great Neice/Nephew
3.13%		 4th Great Neice/Nephew
1.56%		 5th Great Neice/Nephew
0.78%		 6th Great Neice/Nephew
0.39%		 7th Great Neice/Nephew
0.2%		 8th Great Neice/Nephew
0.1%		 9th Great Neice/Nephew
0.05%
Grandparent Niece/Nephew
25%1740cm
1201-2282		 1st Cousin
12.5%866cm
396-1397		 1st Cousin 1x Removed
6.25%433cm
102-980		 1st Cousin 2x Removed
3.13%221cm
33-471		 1st Cousin 3x Removed
1.56%117cm
25-238		 1st Cousin 4x Removed
0.78%		 1st Cousin 5x Removed
0.39%		 1st Cousin 6x Removed
0.2%		 1st Cousin 7x Removed
0.1%		 1st Cousin 8x Removed
0.05%		 1st Cousin 9x Removed
0%
Great-grandparent Great Neice/Nephew
12.5%850cm
330-1467		 1st Cousin 1x Removed
6.25%433cm
102-980		 2nd Cousin
3.13%229cm
41-592		 2nd Cousin 1x Removed
1.56%122cm
14-353		 2nd Cousin 2x Removed
0.78%71cm
0-244		 2nd Cousin 3x Removed
0.39%51cm
0-154		 2nd Cousin 4x Removed
0.2%		 2nd Cousin 5x Removed
0.1%		 2nd Cousin 6x Removed
0.05%		 2nd Cousin 7x Removed
0%		 2nd Cousin 8x Removed
0%
2nd Great-grandparent 2nd Great Neice/Nephew
6.25%420cm
186-713		 1st Cousin 2x Removed
3.13%221cm
33-471		 2nd Cousin 1x Removed
1.56%122cm
14-353		 3rd Cousin
0.78%73cm
0-234		 3rd Cousin 1x Removed
0.39%48cm
0-192		 3rd Cousin 2x Removed
0.2%36cm
0-166		 3rd Cousin 3x Removed
0.1%27cm
0-98		 3rd Cousin 4x Removed
0.05%		 3rd Cousin 5x Removed
0%		 3rd Cousin 6x Removed
0%		 3rd Cousin 7x Removed
0%
3rd Great-grandparent 3rd Great Neice/Nephew
3.13%		 1st Cousin 3x Removed
1.56%117cm
25-238		 2nd Cousin 2x Removed
0.78%71cm
0-244		 3rd Cousin 1x Removed
0.39%48cm
0-192		 4th Cousin
0.2%35cm
0-139		 4th Cousin 1x Removed
0.1%28cm
0-126		 4th Cousin 2x Removed
0.05%22cm
0-93		 4th Cousin 3x Removed
0%19cm
0-60		 4th Cousin 4x Removed
0%		 4th Cousin 5x Removed
0%		 4th Cousin 6x Removed
0%
4th Great-grandparent 4th Great Neice/Nephew
1.56%		 1st Cousin 4x Removed
0.78%		 2nd Cousin 3x Removed
0.39%51cm
0-154		 3rd Cousin 2x Removed
0.2%36cm
0-166		 4th Cousin 1x Removed
0.1%28cm
0-126		 5th Cousin
0.05%25cm
0-117		 5th Cousin 1x Removed
0%21cm
0-80		 5th Cousin 2x Removed
0%18cm
0-65		 5th Cousin 3x Removed
0%13cm
0-30		 5th Cousin 4x Removed
0%		 5th Cousin 5x Removed
0%
5th Great-grandparent 5th Great Neice/Nephew
0.78%		 1st Cousin 5x Removed
0.39%		 2nd Cousin 4x Removed
0.2%		 3rd Cousin 3x Removed
0.1%27cm
0-98		 4th Cousin 2x Removed
0.05%22cm
0-93		 5th Cousin 1x Removed
0%21cm
0-80		 6th Cousin
0%18cm
0-71		 6th Cousin 1x Removed
0%15cm
0-56		 6th Cousin 2x Removed
0%13cm
0-45		 6th Cousin 3x Removed
0%		 6th Cousin 4x Removed
0%
6th Great-grandparent 6th Great Neice/Nephew
0.39%		 1st Cousin 6x Removed
0.2%		 2nd Cousin 5x Removed
0.1%		 3rd Cousin 4x Removed
0.05%		 4th Cousin 3x Removed
0%19cm
0-60		 5th Cousin 2x Removed
0%18cm
0-65		 6th Cousin 1x Removed
0%15cm
0-56		 7th Cousin
0%14cm
0-57		 7th Cousin 1x Removed
0%12cm
0-50		 7th Cousin 2x Removed
0%		 7th Cousin 3x Removed
0%
7th Great-grandparent 7th Great Neice/Nephew
0.2%		 1st Cousin 7x Removed
0.1%		 2nd Cousin 6x Removed
0.05%		 3rd Cousin 5x Removed
0%		 4th Cousin 4x Removed
0%		 5th Cousin 3x Removed
0%13cm
0-30		 6th Cousin 2x Removed
0%13cm
0-45		 7th Cousin 1x Removed
0%12cm
0-50		 8th Cousin
0%11cm
0-42		 8th Cousin 1x Removed
0%		 8th Cousin 2x Removed
0%
8th Great-grandparent 8th Great Neice/Nephew
0.1%		 1st Cousin 8x Removed
0.05%		 2nd Cousin 7x Removed
0%		 3rd Cousin 6x Removed
0%		 4th Cousin 5x Removed
0%		 5th Cousin 4x Removed
0%		 6th Cousin 3x Removed
0%		 7th Cousin 2x Removed
0%		 8th Cousin 1x Removed
0%		 9th Cousin
0%		 9th Cousin 1x Removed
0%
9th Great-grandparent 9th Great Neice/Nephew
0.05%		 1st Cousin 9x Removed
0%		 2nd Cousin 8x Removed
0%		 3rd Cousin 7x Removed
0%		 4th Cousin 6x Removed
0%		 5th Cousin 5x Removed
0%		 6th Cousin 4x Removed
0%		 7th Cousin 3x Removed
0%		 8th Cousin 2x Removed
0%		 9th Cousin 1x Removed
0%		 10th Cousin
0%

*This chart does not include half relationships. DNA estimates decrease when accounting for half relationships and increase in the event of pedigree collapse.
Last Updated: 7/26/2020