Sperm concentration (sometimes called sperm density) is the figure most people have in mind when they talk about a "sperm count". A lab measures it by counting sperm in a known volume of semen under a microscope and scaling up to one millilitre.
It is not the same as total sperm count. Concentration tells you how densely packed sperm are; total count multiplies that by semen volume to give the number in the whole ejaculate. A small, concentrated sample and a large, dilute one can contain the same total number of sperm.
The WHO 2021 lower reference limit is 16 million per mL, the 5th centile among more than 3,500 men whose partners had recently conceived.1 A concentration below the limit is described as oligozoospermia; see oligozoospermia for what that label does and does not mean.
What is a normal sperm concentration?
Anything from 16 million per mL upwards is at or above the WHO lower reference limit. Most fertile men sit well above that, but the limit is a reference point, not a pass mark.
Reference limits describe the bottom 5% of a fertile population. The authors of the 2021 figures stress that they are not distinct limits between fertile and subfertile men.1 A man at 14 million per mL is not infertile, and a man at 20 million per mL is not guaranteed to conceive quickly.
Your result is always read alongside motility, morphology, volume and, crucially, your partner's fertility.
Does a higher sperm concentration mean better fertility?
Up to a point. In one large study, pregnancy chances rose with concentration until about 40 million per mL, and higher concentrations added nothing further.
In a Danish study of 430 couples trying for their first baby, the chance of conceiving rose with sperm concentration up to 40 million per mL; higher concentrations did not improve the odds further.2 Pregnancies occurred in 65.0% of couples where the man was at or above 40 million per mL and 51.2% of those below it.2
A larger US study compared 696 fertile and 765 infertile men.3 It classed concentrations below 13.5 million per mL as subfertile, above 48 million as fertile, and those in between as indeterminate. The key caveat: there was extensive overlap between fertile and infertile men in every range, and the authors concluded that no single measure is diagnostic of infertility.3
Why can concentration change so much between samples?
Sperm numbers naturally swing from one ejaculate to the next, even in healthy men. A single result, high or low, is a snapshot rather than a fixed trait.
In a study of men who each gave at least five samples, sperm count was the most variable of all the measures, with typical within-man variation of around 46% to 54%.4 The same study suggested at least three samples are needed for a reliable estimate.4
Things that can shift a result include how long it has been since you last ejaculated (see ejaculatory abstinence), whether any of the sample was lost, and your general health in the weeks before, since sperm take a couple of months to develop. Our post on how long sperm take to regenerate explains the timeline.
- Follow the lab's abstinence instructions exactly.
- Collect the whole ejaculate; tell the lab if any is missed.
- Mention recent illness or new medicines when you hand the sample in.
Common questions
What is a good sperm concentration for getting pregnant?
There is no single cut-off, but studies suggest the odds of conception rise up to roughly 40 million per mL and level off after that.2 Concentrations between the WHO limit and that level are common in men who conceive without help.
Is 15 million sperm per mL too low?
It is just below the WHO 2021 lower reference limit of 16 million per mL, so it would be flagged.1 That is a reason to repeat the test and look at the other results, not a diagnosis of infertility.
Does sperm concentration go up if you ejaculate less often?
The length of time since you last ejaculated does change semen results, but longer is not simply better. Labs set a specific abstinence window so results can be compared; follow it rather than saving up.
Read more on this
Lifestyle factors that affect male fertility: a practical guide
How long does it take sperm to regenerate?
Sources
- Campbell MJ, Lotti F, Baldi E, et al. Distribution of semen examination results 2020 - A follow up of data collated for the WHO semen analysis manual 2010. Andrology. 2021;9(3):817-822. PubMed
- Bonde JP, Ernst E, Jensen TK, et al. Relation between semen quality and fertility: a population-based study of 430 first-pregnancy planners. Lancet. 1998;352(9135):1172-1177. PubMed
- Guzick DS, Overstreet JW, Factor-Litvak P, et al. Sperm morphology, motility, and concentration in fertile and infertile men. N Engl J Med. 2001;345(19):1388-1393. PubMed
- Keel BA. Within- and between-subject variation in semen parameters in infertile men and normal semen donors. Fertil Steril. 2006;85(1):128-134. PubMed
Not medical advice. Written by Eric Stephens from the research cited above; not reviewed by a doctor. If something worries you, see a GP.